Find trigonometric form of complex number $frac{1}{2}-frac{1}{sqrt{2}}i$












-1












$begingroup$


Find trigonometric form of complex number $frac{1}{2}-frac{1}{sqrt{2}}i$.



I assume that this is related to trigonometric form of complex number



$$1 pm cos(alpha) pm isin(alpha)$$ or similiar.



Is it possible to find such form without taking arctangent?










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  • 1




    $begingroup$
    Why the $1$? Why not $r(cosalpha+isinalpha)$?
    $endgroup$
    – Lord Shark the Unknown
    Jan 8 at 19:16










  • $begingroup$
    hint: find modulus first then divide real part by modulus to get cosine, divide imaginary part by modulus to get sine
    $endgroup$
    – Vasya
    Jan 8 at 19:16






  • 1




    $begingroup$
    What's wrong with taking the arctangent? You can divide the result by $pi$ to so if the result is a nice fraction (it isn't). You can draw a picture and do some symilar triangle relationship chasing but I don't think you get any "nice" angles.
    $endgroup$
    – fleablood
    Jan 8 at 19:50










  • $begingroup$
    Our professor told us to do so, but I suppose there must be mistake if such "horrible" angles occur.
    $endgroup$
    – janusz
    Jan 8 at 19:52
















-1












$begingroup$


Find trigonometric form of complex number $frac{1}{2}-frac{1}{sqrt{2}}i$.



I assume that this is related to trigonometric form of complex number



$$1 pm cos(alpha) pm isin(alpha)$$ or similiar.



Is it possible to find such form without taking arctangent?










share|cite|improve this question











$endgroup$








  • 1




    $begingroup$
    Why the $1$? Why not $r(cosalpha+isinalpha)$?
    $endgroup$
    – Lord Shark the Unknown
    Jan 8 at 19:16










  • $begingroup$
    hint: find modulus first then divide real part by modulus to get cosine, divide imaginary part by modulus to get sine
    $endgroup$
    – Vasya
    Jan 8 at 19:16






  • 1




    $begingroup$
    What's wrong with taking the arctangent? You can divide the result by $pi$ to so if the result is a nice fraction (it isn't). You can draw a picture and do some symilar triangle relationship chasing but I don't think you get any "nice" angles.
    $endgroup$
    – fleablood
    Jan 8 at 19:50










  • $begingroup$
    Our professor told us to do so, but I suppose there must be mistake if such "horrible" angles occur.
    $endgroup$
    – janusz
    Jan 8 at 19:52














-1












-1








-1





$begingroup$


Find trigonometric form of complex number $frac{1}{2}-frac{1}{sqrt{2}}i$.



I assume that this is related to trigonometric form of complex number



$$1 pm cos(alpha) pm isin(alpha)$$ or similiar.



Is it possible to find such form without taking arctangent?










share|cite|improve this question











$endgroup$




Find trigonometric form of complex number $frac{1}{2}-frac{1}{sqrt{2}}i$.



I assume that this is related to trigonometric form of complex number



$$1 pm cos(alpha) pm isin(alpha)$$ or similiar.



Is it possible to find such form without taking arctangent?







complex-numbers






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Jan 8 at 19:22







janusz

















asked Jan 8 at 19:14









januszjanusz

474210




474210








  • 1




    $begingroup$
    Why the $1$? Why not $r(cosalpha+isinalpha)$?
    $endgroup$
    – Lord Shark the Unknown
    Jan 8 at 19:16










  • $begingroup$
    hint: find modulus first then divide real part by modulus to get cosine, divide imaginary part by modulus to get sine
    $endgroup$
    – Vasya
    Jan 8 at 19:16






  • 1




    $begingroup$
    What's wrong with taking the arctangent? You can divide the result by $pi$ to so if the result is a nice fraction (it isn't). You can draw a picture and do some symilar triangle relationship chasing but I don't think you get any "nice" angles.
    $endgroup$
    – fleablood
    Jan 8 at 19:50










  • $begingroup$
    Our professor told us to do so, but I suppose there must be mistake if such "horrible" angles occur.
    $endgroup$
    – janusz
    Jan 8 at 19:52














  • 1




    $begingroup$
    Why the $1$? Why not $r(cosalpha+isinalpha)$?
    $endgroup$
    – Lord Shark the Unknown
    Jan 8 at 19:16










  • $begingroup$
    hint: find modulus first then divide real part by modulus to get cosine, divide imaginary part by modulus to get sine
    $endgroup$
    – Vasya
    Jan 8 at 19:16






  • 1




    $begingroup$
    What's wrong with taking the arctangent? You can divide the result by $pi$ to so if the result is a nice fraction (it isn't). You can draw a picture and do some symilar triangle relationship chasing but I don't think you get any "nice" angles.
    $endgroup$
    – fleablood
    Jan 8 at 19:50










  • $begingroup$
    Our professor told us to do so, but I suppose there must be mistake if such "horrible" angles occur.
    $endgroup$
    – janusz
    Jan 8 at 19:52








1




1




$begingroup$
Why the $1$? Why not $r(cosalpha+isinalpha)$?
$endgroup$
– Lord Shark the Unknown
Jan 8 at 19:16




$begingroup$
Why the $1$? Why not $r(cosalpha+isinalpha)$?
$endgroup$
– Lord Shark the Unknown
Jan 8 at 19:16












$begingroup$
hint: find modulus first then divide real part by modulus to get cosine, divide imaginary part by modulus to get sine
$endgroup$
– Vasya
Jan 8 at 19:16




$begingroup$
hint: find modulus first then divide real part by modulus to get cosine, divide imaginary part by modulus to get sine
$endgroup$
– Vasya
Jan 8 at 19:16




1




1




$begingroup$
What's wrong with taking the arctangent? You can divide the result by $pi$ to so if the result is a nice fraction (it isn't). You can draw a picture and do some symilar triangle relationship chasing but I don't think you get any "nice" angles.
$endgroup$
– fleablood
Jan 8 at 19:50




$begingroup$
What's wrong with taking the arctangent? You can divide the result by $pi$ to so if the result is a nice fraction (it isn't). You can draw a picture and do some symilar triangle relationship chasing but I don't think you get any "nice" angles.
$endgroup$
– fleablood
Jan 8 at 19:50












$begingroup$
Our professor told us to do so, but I suppose there must be mistake if such "horrible" angles occur.
$endgroup$
– janusz
Jan 8 at 19:52




$begingroup$
Our professor told us to do so, but I suppose there must be mistake if such "horrible" angles occur.
$endgroup$
– janusz
Jan 8 at 19:52










4 Answers
4






active

oldest

votes


















2












$begingroup$

Just do it.



$|frac 12 - frac 1{sqrt 2} i| = sqrt {frac 12^2 + frac 12} = frac {sqrt 3} 2$



So $frac 12 - frac 1{sqrt 2} i = frac {sqrt 3}2 (frac 1{sqrt 3} - frac {sqrt 2}{sqrt 3}i)$



$frac {1}{sqrt 3}^2 + (-frac {sqrt 2}{sqrt 3})^2 = 1$ so there exists a unique $theta$ ($0 le theta < 2pi$) so that $cos theta = frac 1{sqrt 3}$ and $sin theta = -frac {sqrt 2}{sqrt 3}$.



In that case $tan theta = frac {sin theta}{cos theta} = frac {-frac {sqrt 2}{sqrt 3}}{frac 1{sqrt 3}} = -{sqrt 2}$.



So $theta$ would be $arctan {-sqrt 2}$ with some possible linear transformation to put it in the proper (4th) quadrant. As $arctan$ returns values from $-frac pi 2$ to $ frac pi 2$ (the 4th and 1st quadrant) we are good.



$theta = arctan{-sqrt 2} = -0.304087... pi$. Which so far as I can tell has no rational interpretation.



So $ frac 12 - frac 1{sqrt 2} i = frac {sqrt 3}2(cos arctan{-sqrt 2} + sin arctan{-sqrt 2} i) = frac {sqrt 3}2e^{iarctan{-sqrt 2}}$






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    1












    $begingroup$

    You should write in form $$ z= |z|(cos alpha +isin alpha)$$



    The modulus $$|z| = sqrt{{1over 4}+{1over 2}} = {sqrt{3}over2}$$



    Since $sin alpha = -{sqrt{2}over sqrt{3}}$ and $cos alpha = -{1over 2sqrt{3}}$ and you will get an $alpha$ by solving this system.






    share|cite|improve this answer









    $endgroup$













    • $begingroup$
      I've edited my question, sorry
      $endgroup$
      – janusz
      Jan 8 at 19:24










    • $begingroup$
      Yes, you can by drawing $z$ in complex plane, but you will get not an exact value of argument.
      $endgroup$
      – Maria Mazur
      Jan 8 at 19:26



















    1












    $begingroup$

    HINT



    You have
    $$
    re^{it} = rleft(cos t + isin tright),
    $$

    and note that
    $$
    r^2 = left(frac12right)^2+left(frac1{sqrt2}right)^2 = frac34,
    $$

    can you find $t$?






    share|cite|improve this answer











    $endgroup$













    • $begingroup$
      I've edited my question, sorry
      $endgroup$
      – janusz
      Jan 8 at 19:24






    • 1




      $begingroup$
      Your first equation is only true if $r=1$. You omitted $r$ on the RHS.
      $endgroup$
      – MPW
      Jan 8 at 19:28










    • $begingroup$
      @MPW corrected, sorry for the typo
      $endgroup$
      – gt6989b
      Jan 8 at 20:58



















    1












    $begingroup$

    In general any complex number $z=x+iy$ can be represented as $re^{itheta}$ where begin{equation} r^2 = |z|^2 = x^2+y^2end{equation} and begin{equation} theta = tan^{-1} Bigl(frac{y}{x}Bigr)end{equation}



    Here, begin{equation}
    r = sqrt{frac{1}{4}+frac{1}{2}} = frac{sqrt{3}}{2}end{equation}

    begin{equation}
    theta = tan^{-1}Bigl(frac{-frac{1}{sqrt{2}}}{frac{1}{2}}Bigr) = tan^{-1}(-sqrt{2})
    end{equation}

    Here, since $ costheta > 0 $ and $ sintheta <0, theta $ is in fourth quadrant. Thus, $ frac{3π}{2}lethetale2π $ or simply,
    $theta = -tan^{-1} (sqrt{2})$



    Now assume that begin{equation}
    tan{x} = u
    end{equation}

    Thus, begin{equation}
    cos = sqrt{frac{1}{1+u^2}}
    end{equation}

    Thus,
    begin{equation}
    x = tan^{-1} (u) = cos^{-1}Bigl(sqrt{frac{1}{1+u^2}}Bigr)
    end{equation}

    Thus,
    begin{equation}
    cos(tan^{-1} (u)) = frac{1}{sqrt{1+u^2}}
    end{equation}

    Thus,
    begin{equation} cos(tan^{-1}(-sqrt{2})) = frac{1}{sqrt{3}}end{equation}
    Thus,begin{equation} sin{theta} =- sqrt{frac{2}{3}}end{equation}






    share|cite|improve this answer











    $endgroup$













    • $begingroup$
      Just a slight slip: our point is in the fourth quadrant of the Gaussian plane, so the sine has to be negative.
      $endgroup$
      – Lubin
      Jan 9 at 2:09










    • $begingroup$
      Yes. I am so sorry for that Lubin
      $endgroup$
      – John Brookfields
      Jan 10 at 7:30












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    4 Answers
    4






    active

    oldest

    votes








    4 Answers
    4






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    2












    $begingroup$

    Just do it.



    $|frac 12 - frac 1{sqrt 2} i| = sqrt {frac 12^2 + frac 12} = frac {sqrt 3} 2$



    So $frac 12 - frac 1{sqrt 2} i = frac {sqrt 3}2 (frac 1{sqrt 3} - frac {sqrt 2}{sqrt 3}i)$



    $frac {1}{sqrt 3}^2 + (-frac {sqrt 2}{sqrt 3})^2 = 1$ so there exists a unique $theta$ ($0 le theta < 2pi$) so that $cos theta = frac 1{sqrt 3}$ and $sin theta = -frac {sqrt 2}{sqrt 3}$.



    In that case $tan theta = frac {sin theta}{cos theta} = frac {-frac {sqrt 2}{sqrt 3}}{frac 1{sqrt 3}} = -{sqrt 2}$.



    So $theta$ would be $arctan {-sqrt 2}$ with some possible linear transformation to put it in the proper (4th) quadrant. As $arctan$ returns values from $-frac pi 2$ to $ frac pi 2$ (the 4th and 1st quadrant) we are good.



    $theta = arctan{-sqrt 2} = -0.304087... pi$. Which so far as I can tell has no rational interpretation.



    So $ frac 12 - frac 1{sqrt 2} i = frac {sqrt 3}2(cos arctan{-sqrt 2} + sin arctan{-sqrt 2} i) = frac {sqrt 3}2e^{iarctan{-sqrt 2}}$






    share|cite|improve this answer









    $endgroup$


















      2












      $begingroup$

      Just do it.



      $|frac 12 - frac 1{sqrt 2} i| = sqrt {frac 12^2 + frac 12} = frac {sqrt 3} 2$



      So $frac 12 - frac 1{sqrt 2} i = frac {sqrt 3}2 (frac 1{sqrt 3} - frac {sqrt 2}{sqrt 3}i)$



      $frac {1}{sqrt 3}^2 + (-frac {sqrt 2}{sqrt 3})^2 = 1$ so there exists a unique $theta$ ($0 le theta < 2pi$) so that $cos theta = frac 1{sqrt 3}$ and $sin theta = -frac {sqrt 2}{sqrt 3}$.



      In that case $tan theta = frac {sin theta}{cos theta} = frac {-frac {sqrt 2}{sqrt 3}}{frac 1{sqrt 3}} = -{sqrt 2}$.



      So $theta$ would be $arctan {-sqrt 2}$ with some possible linear transformation to put it in the proper (4th) quadrant. As $arctan$ returns values from $-frac pi 2$ to $ frac pi 2$ (the 4th and 1st quadrant) we are good.



      $theta = arctan{-sqrt 2} = -0.304087... pi$. Which so far as I can tell has no rational interpretation.



      So $ frac 12 - frac 1{sqrt 2} i = frac {sqrt 3}2(cos arctan{-sqrt 2} + sin arctan{-sqrt 2} i) = frac {sqrt 3}2e^{iarctan{-sqrt 2}}$






      share|cite|improve this answer









      $endgroup$
















        2












        2








        2





        $begingroup$

        Just do it.



        $|frac 12 - frac 1{sqrt 2} i| = sqrt {frac 12^2 + frac 12} = frac {sqrt 3} 2$



        So $frac 12 - frac 1{sqrt 2} i = frac {sqrt 3}2 (frac 1{sqrt 3} - frac {sqrt 2}{sqrt 3}i)$



        $frac {1}{sqrt 3}^2 + (-frac {sqrt 2}{sqrt 3})^2 = 1$ so there exists a unique $theta$ ($0 le theta < 2pi$) so that $cos theta = frac 1{sqrt 3}$ and $sin theta = -frac {sqrt 2}{sqrt 3}$.



        In that case $tan theta = frac {sin theta}{cos theta} = frac {-frac {sqrt 2}{sqrt 3}}{frac 1{sqrt 3}} = -{sqrt 2}$.



        So $theta$ would be $arctan {-sqrt 2}$ with some possible linear transformation to put it in the proper (4th) quadrant. As $arctan$ returns values from $-frac pi 2$ to $ frac pi 2$ (the 4th and 1st quadrant) we are good.



        $theta = arctan{-sqrt 2} = -0.304087... pi$. Which so far as I can tell has no rational interpretation.



        So $ frac 12 - frac 1{sqrt 2} i = frac {sqrt 3}2(cos arctan{-sqrt 2} + sin arctan{-sqrt 2} i) = frac {sqrt 3}2e^{iarctan{-sqrt 2}}$






        share|cite|improve this answer









        $endgroup$



        Just do it.



        $|frac 12 - frac 1{sqrt 2} i| = sqrt {frac 12^2 + frac 12} = frac {sqrt 3} 2$



        So $frac 12 - frac 1{sqrt 2} i = frac {sqrt 3}2 (frac 1{sqrt 3} - frac {sqrt 2}{sqrt 3}i)$



        $frac {1}{sqrt 3}^2 + (-frac {sqrt 2}{sqrt 3})^2 = 1$ so there exists a unique $theta$ ($0 le theta < 2pi$) so that $cos theta = frac 1{sqrt 3}$ and $sin theta = -frac {sqrt 2}{sqrt 3}$.



        In that case $tan theta = frac {sin theta}{cos theta} = frac {-frac {sqrt 2}{sqrt 3}}{frac 1{sqrt 3}} = -{sqrt 2}$.



        So $theta$ would be $arctan {-sqrt 2}$ with some possible linear transformation to put it in the proper (4th) quadrant. As $arctan$ returns values from $-frac pi 2$ to $ frac pi 2$ (the 4th and 1st quadrant) we are good.



        $theta = arctan{-sqrt 2} = -0.304087... pi$. Which so far as I can tell has no rational interpretation.



        So $ frac 12 - frac 1{sqrt 2} i = frac {sqrt 3}2(cos arctan{-sqrt 2} + sin arctan{-sqrt 2} i) = frac {sqrt 3}2e^{iarctan{-sqrt 2}}$







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Jan 8 at 19:47









        fleabloodfleablood

        1




        1























            1












            $begingroup$

            You should write in form $$ z= |z|(cos alpha +isin alpha)$$



            The modulus $$|z| = sqrt{{1over 4}+{1over 2}} = {sqrt{3}over2}$$



            Since $sin alpha = -{sqrt{2}over sqrt{3}}$ and $cos alpha = -{1over 2sqrt{3}}$ and you will get an $alpha$ by solving this system.






            share|cite|improve this answer









            $endgroup$













            • $begingroup$
              I've edited my question, sorry
              $endgroup$
              – janusz
              Jan 8 at 19:24










            • $begingroup$
              Yes, you can by drawing $z$ in complex plane, but you will get not an exact value of argument.
              $endgroup$
              – Maria Mazur
              Jan 8 at 19:26
















            1












            $begingroup$

            You should write in form $$ z= |z|(cos alpha +isin alpha)$$



            The modulus $$|z| = sqrt{{1over 4}+{1over 2}} = {sqrt{3}over2}$$



            Since $sin alpha = -{sqrt{2}over sqrt{3}}$ and $cos alpha = -{1over 2sqrt{3}}$ and you will get an $alpha$ by solving this system.






            share|cite|improve this answer









            $endgroup$













            • $begingroup$
              I've edited my question, sorry
              $endgroup$
              – janusz
              Jan 8 at 19:24










            • $begingroup$
              Yes, you can by drawing $z$ in complex plane, but you will get not an exact value of argument.
              $endgroup$
              – Maria Mazur
              Jan 8 at 19:26














            1












            1








            1





            $begingroup$

            You should write in form $$ z= |z|(cos alpha +isin alpha)$$



            The modulus $$|z| = sqrt{{1over 4}+{1over 2}} = {sqrt{3}over2}$$



            Since $sin alpha = -{sqrt{2}over sqrt{3}}$ and $cos alpha = -{1over 2sqrt{3}}$ and you will get an $alpha$ by solving this system.






            share|cite|improve this answer









            $endgroup$



            You should write in form $$ z= |z|(cos alpha +isin alpha)$$



            The modulus $$|z| = sqrt{{1over 4}+{1over 2}} = {sqrt{3}over2}$$



            Since $sin alpha = -{sqrt{2}over sqrt{3}}$ and $cos alpha = -{1over 2sqrt{3}}$ and you will get an $alpha$ by solving this system.







            share|cite|improve this answer












            share|cite|improve this answer



            share|cite|improve this answer










            answered Jan 8 at 19:17









            Maria MazurMaria Mazur

            50k1361125




            50k1361125












            • $begingroup$
              I've edited my question, sorry
              $endgroup$
              – janusz
              Jan 8 at 19:24










            • $begingroup$
              Yes, you can by drawing $z$ in complex plane, but you will get not an exact value of argument.
              $endgroup$
              – Maria Mazur
              Jan 8 at 19:26


















            • $begingroup$
              I've edited my question, sorry
              $endgroup$
              – janusz
              Jan 8 at 19:24










            • $begingroup$
              Yes, you can by drawing $z$ in complex plane, but you will get not an exact value of argument.
              $endgroup$
              – Maria Mazur
              Jan 8 at 19:26
















            $begingroup$
            I've edited my question, sorry
            $endgroup$
            – janusz
            Jan 8 at 19:24




            $begingroup$
            I've edited my question, sorry
            $endgroup$
            – janusz
            Jan 8 at 19:24












            $begingroup$
            Yes, you can by drawing $z$ in complex plane, but you will get not an exact value of argument.
            $endgroup$
            – Maria Mazur
            Jan 8 at 19:26




            $begingroup$
            Yes, you can by drawing $z$ in complex plane, but you will get not an exact value of argument.
            $endgroup$
            – Maria Mazur
            Jan 8 at 19:26











            1












            $begingroup$

            HINT



            You have
            $$
            re^{it} = rleft(cos t + isin tright),
            $$

            and note that
            $$
            r^2 = left(frac12right)^2+left(frac1{sqrt2}right)^2 = frac34,
            $$

            can you find $t$?






            share|cite|improve this answer











            $endgroup$













            • $begingroup$
              I've edited my question, sorry
              $endgroup$
              – janusz
              Jan 8 at 19:24






            • 1




              $begingroup$
              Your first equation is only true if $r=1$. You omitted $r$ on the RHS.
              $endgroup$
              – MPW
              Jan 8 at 19:28










            • $begingroup$
              @MPW corrected, sorry for the typo
              $endgroup$
              – gt6989b
              Jan 8 at 20:58
















            1












            $begingroup$

            HINT



            You have
            $$
            re^{it} = rleft(cos t + isin tright),
            $$

            and note that
            $$
            r^2 = left(frac12right)^2+left(frac1{sqrt2}right)^2 = frac34,
            $$

            can you find $t$?






            share|cite|improve this answer











            $endgroup$













            • $begingroup$
              I've edited my question, sorry
              $endgroup$
              – janusz
              Jan 8 at 19:24






            • 1




              $begingroup$
              Your first equation is only true if $r=1$. You omitted $r$ on the RHS.
              $endgroup$
              – MPW
              Jan 8 at 19:28










            • $begingroup$
              @MPW corrected, sorry for the typo
              $endgroup$
              – gt6989b
              Jan 8 at 20:58














            1












            1








            1





            $begingroup$

            HINT



            You have
            $$
            re^{it} = rleft(cos t + isin tright),
            $$

            and note that
            $$
            r^2 = left(frac12right)^2+left(frac1{sqrt2}right)^2 = frac34,
            $$

            can you find $t$?






            share|cite|improve this answer











            $endgroup$



            HINT



            You have
            $$
            re^{it} = rleft(cos t + isin tright),
            $$

            and note that
            $$
            r^2 = left(frac12right)^2+left(frac1{sqrt2}right)^2 = frac34,
            $$

            can you find $t$?







            share|cite|improve this answer














            share|cite|improve this answer



            share|cite|improve this answer








            edited Jan 8 at 20:58

























            answered Jan 8 at 19:18









            gt6989bgt6989b

            35.8k22557




            35.8k22557












            • $begingroup$
              I've edited my question, sorry
              $endgroup$
              – janusz
              Jan 8 at 19:24






            • 1




              $begingroup$
              Your first equation is only true if $r=1$. You omitted $r$ on the RHS.
              $endgroup$
              – MPW
              Jan 8 at 19:28










            • $begingroup$
              @MPW corrected, sorry for the typo
              $endgroup$
              – gt6989b
              Jan 8 at 20:58


















            • $begingroup$
              I've edited my question, sorry
              $endgroup$
              – janusz
              Jan 8 at 19:24






            • 1




              $begingroup$
              Your first equation is only true if $r=1$. You omitted $r$ on the RHS.
              $endgroup$
              – MPW
              Jan 8 at 19:28










            • $begingroup$
              @MPW corrected, sorry for the typo
              $endgroup$
              – gt6989b
              Jan 8 at 20:58
















            $begingroup$
            I've edited my question, sorry
            $endgroup$
            – janusz
            Jan 8 at 19:24




            $begingroup$
            I've edited my question, sorry
            $endgroup$
            – janusz
            Jan 8 at 19:24




            1




            1




            $begingroup$
            Your first equation is only true if $r=1$. You omitted $r$ on the RHS.
            $endgroup$
            – MPW
            Jan 8 at 19:28




            $begingroup$
            Your first equation is only true if $r=1$. You omitted $r$ on the RHS.
            $endgroup$
            – MPW
            Jan 8 at 19:28












            $begingroup$
            @MPW corrected, sorry for the typo
            $endgroup$
            – gt6989b
            Jan 8 at 20:58




            $begingroup$
            @MPW corrected, sorry for the typo
            $endgroup$
            – gt6989b
            Jan 8 at 20:58











            1












            $begingroup$

            In general any complex number $z=x+iy$ can be represented as $re^{itheta}$ where begin{equation} r^2 = |z|^2 = x^2+y^2end{equation} and begin{equation} theta = tan^{-1} Bigl(frac{y}{x}Bigr)end{equation}



            Here, begin{equation}
            r = sqrt{frac{1}{4}+frac{1}{2}} = frac{sqrt{3}}{2}end{equation}

            begin{equation}
            theta = tan^{-1}Bigl(frac{-frac{1}{sqrt{2}}}{frac{1}{2}}Bigr) = tan^{-1}(-sqrt{2})
            end{equation}

            Here, since $ costheta > 0 $ and $ sintheta <0, theta $ is in fourth quadrant. Thus, $ frac{3π}{2}lethetale2π $ or simply,
            $theta = -tan^{-1} (sqrt{2})$



            Now assume that begin{equation}
            tan{x} = u
            end{equation}

            Thus, begin{equation}
            cos = sqrt{frac{1}{1+u^2}}
            end{equation}

            Thus,
            begin{equation}
            x = tan^{-1} (u) = cos^{-1}Bigl(sqrt{frac{1}{1+u^2}}Bigr)
            end{equation}

            Thus,
            begin{equation}
            cos(tan^{-1} (u)) = frac{1}{sqrt{1+u^2}}
            end{equation}

            Thus,
            begin{equation} cos(tan^{-1}(-sqrt{2})) = frac{1}{sqrt{3}}end{equation}
            Thus,begin{equation} sin{theta} =- sqrt{frac{2}{3}}end{equation}






            share|cite|improve this answer











            $endgroup$













            • $begingroup$
              Just a slight slip: our point is in the fourth quadrant of the Gaussian plane, so the sine has to be negative.
              $endgroup$
              – Lubin
              Jan 9 at 2:09










            • $begingroup$
              Yes. I am so sorry for that Lubin
              $endgroup$
              – John Brookfields
              Jan 10 at 7:30
















            1












            $begingroup$

            In general any complex number $z=x+iy$ can be represented as $re^{itheta}$ where begin{equation} r^2 = |z|^2 = x^2+y^2end{equation} and begin{equation} theta = tan^{-1} Bigl(frac{y}{x}Bigr)end{equation}



            Here, begin{equation}
            r = sqrt{frac{1}{4}+frac{1}{2}} = frac{sqrt{3}}{2}end{equation}

            begin{equation}
            theta = tan^{-1}Bigl(frac{-frac{1}{sqrt{2}}}{frac{1}{2}}Bigr) = tan^{-1}(-sqrt{2})
            end{equation}

            Here, since $ costheta > 0 $ and $ sintheta <0, theta $ is in fourth quadrant. Thus, $ frac{3π}{2}lethetale2π $ or simply,
            $theta = -tan^{-1} (sqrt{2})$



            Now assume that begin{equation}
            tan{x} = u
            end{equation}

            Thus, begin{equation}
            cos = sqrt{frac{1}{1+u^2}}
            end{equation}

            Thus,
            begin{equation}
            x = tan^{-1} (u) = cos^{-1}Bigl(sqrt{frac{1}{1+u^2}}Bigr)
            end{equation}

            Thus,
            begin{equation}
            cos(tan^{-1} (u)) = frac{1}{sqrt{1+u^2}}
            end{equation}

            Thus,
            begin{equation} cos(tan^{-1}(-sqrt{2})) = frac{1}{sqrt{3}}end{equation}
            Thus,begin{equation} sin{theta} =- sqrt{frac{2}{3}}end{equation}






            share|cite|improve this answer











            $endgroup$













            • $begingroup$
              Just a slight slip: our point is in the fourth quadrant of the Gaussian plane, so the sine has to be negative.
              $endgroup$
              – Lubin
              Jan 9 at 2:09










            • $begingroup$
              Yes. I am so sorry for that Lubin
              $endgroup$
              – John Brookfields
              Jan 10 at 7:30














            1












            1








            1





            $begingroup$

            In general any complex number $z=x+iy$ can be represented as $re^{itheta}$ where begin{equation} r^2 = |z|^2 = x^2+y^2end{equation} and begin{equation} theta = tan^{-1} Bigl(frac{y}{x}Bigr)end{equation}



            Here, begin{equation}
            r = sqrt{frac{1}{4}+frac{1}{2}} = frac{sqrt{3}}{2}end{equation}

            begin{equation}
            theta = tan^{-1}Bigl(frac{-frac{1}{sqrt{2}}}{frac{1}{2}}Bigr) = tan^{-1}(-sqrt{2})
            end{equation}

            Here, since $ costheta > 0 $ and $ sintheta <0, theta $ is in fourth quadrant. Thus, $ frac{3π}{2}lethetale2π $ or simply,
            $theta = -tan^{-1} (sqrt{2})$



            Now assume that begin{equation}
            tan{x} = u
            end{equation}

            Thus, begin{equation}
            cos = sqrt{frac{1}{1+u^2}}
            end{equation}

            Thus,
            begin{equation}
            x = tan^{-1} (u) = cos^{-1}Bigl(sqrt{frac{1}{1+u^2}}Bigr)
            end{equation}

            Thus,
            begin{equation}
            cos(tan^{-1} (u)) = frac{1}{sqrt{1+u^2}}
            end{equation}

            Thus,
            begin{equation} cos(tan^{-1}(-sqrt{2})) = frac{1}{sqrt{3}}end{equation}
            Thus,begin{equation} sin{theta} =- sqrt{frac{2}{3}}end{equation}






            share|cite|improve this answer











            $endgroup$



            In general any complex number $z=x+iy$ can be represented as $re^{itheta}$ where begin{equation} r^2 = |z|^2 = x^2+y^2end{equation} and begin{equation} theta = tan^{-1} Bigl(frac{y}{x}Bigr)end{equation}



            Here, begin{equation}
            r = sqrt{frac{1}{4}+frac{1}{2}} = frac{sqrt{3}}{2}end{equation}

            begin{equation}
            theta = tan^{-1}Bigl(frac{-frac{1}{sqrt{2}}}{frac{1}{2}}Bigr) = tan^{-1}(-sqrt{2})
            end{equation}

            Here, since $ costheta > 0 $ and $ sintheta <0, theta $ is in fourth quadrant. Thus, $ frac{3π}{2}lethetale2π $ or simply,
            $theta = -tan^{-1} (sqrt{2})$



            Now assume that begin{equation}
            tan{x} = u
            end{equation}

            Thus, begin{equation}
            cos = sqrt{frac{1}{1+u^2}}
            end{equation}

            Thus,
            begin{equation}
            x = tan^{-1} (u) = cos^{-1}Bigl(sqrt{frac{1}{1+u^2}}Bigr)
            end{equation}

            Thus,
            begin{equation}
            cos(tan^{-1} (u)) = frac{1}{sqrt{1+u^2}}
            end{equation}

            Thus,
            begin{equation} cos(tan^{-1}(-sqrt{2})) = frac{1}{sqrt{3}}end{equation}
            Thus,begin{equation} sin{theta} =- sqrt{frac{2}{3}}end{equation}







            share|cite|improve this answer














            share|cite|improve this answer



            share|cite|improve this answer








            edited Jan 10 at 7:37

























            answered Jan 8 at 19:35









            John BrookfieldsJohn Brookfields

            213




            213












            • $begingroup$
              Just a slight slip: our point is in the fourth quadrant of the Gaussian plane, so the sine has to be negative.
              $endgroup$
              – Lubin
              Jan 9 at 2:09










            • $begingroup$
              Yes. I am so sorry for that Lubin
              $endgroup$
              – John Brookfields
              Jan 10 at 7:30


















            • $begingroup$
              Just a slight slip: our point is in the fourth quadrant of the Gaussian plane, so the sine has to be negative.
              $endgroup$
              – Lubin
              Jan 9 at 2:09










            • $begingroup$
              Yes. I am so sorry for that Lubin
              $endgroup$
              – John Brookfields
              Jan 10 at 7:30
















            $begingroup$
            Just a slight slip: our point is in the fourth quadrant of the Gaussian plane, so the sine has to be negative.
            $endgroup$
            – Lubin
            Jan 9 at 2:09




            $begingroup$
            Just a slight slip: our point is in the fourth quadrant of the Gaussian plane, so the sine has to be negative.
            $endgroup$
            – Lubin
            Jan 9 at 2:09












            $begingroup$
            Yes. I am so sorry for that Lubin
            $endgroup$
            – John Brookfields
            Jan 10 at 7:30




            $begingroup$
            Yes. I am so sorry for that Lubin
            $endgroup$
            – John Brookfields
            Jan 10 at 7:30


















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