Algebra Mess, don't know how to proceed
$begingroup$
I have kind of an algebra problem. The original question is a Bilinear transformation for analogue to digital filters.
(This is not a homework question)
In my lecture notes, he goes to the answer like 1 step,
I'm trying to work it out but I'm getting stuck at one place and I don't know how to proceed to get the same way he has it.
algebra-precalculus
$endgroup$
add a comment |
$begingroup$
I have kind of an algebra problem. The original question is a Bilinear transformation for analogue to digital filters.
(This is not a homework question)
In my lecture notes, he goes to the answer like 1 step,
I'm trying to work it out but I'm getting stuck at one place and I don't know how to proceed to get the same way he has it.
algebra-precalculus
$endgroup$
$begingroup$
Multiply the numerator and the denominator by $(1+z^{-1})^3$ to get the cancellation that you are looking for and multiply it out. Often lecturers will shave some time off the presentation by skipping the tedious steps expecting that students can do the multiplication on their own time. It's likely that what was presented as one step took a few more steps but just weren't shown.
$endgroup$
– Mason
Dec 11 '18 at 23:46
add a comment |
$begingroup$
I have kind of an algebra problem. The original question is a Bilinear transformation for analogue to digital filters.
(This is not a homework question)
In my lecture notes, he goes to the answer like 1 step,
I'm trying to work it out but I'm getting stuck at one place and I don't know how to proceed to get the same way he has it.
algebra-precalculus
$endgroup$
I have kind of an algebra problem. The original question is a Bilinear transformation for analogue to digital filters.
(This is not a homework question)
In my lecture notes, he goes to the answer like 1 step,
I'm trying to work it out but I'm getting stuck at one place and I don't know how to proceed to get the same way he has it.
algebra-precalculus
algebra-precalculus
edited Dec 11 '18 at 23:50
Blue
48.4k870154
48.4k870154
asked Dec 11 '18 at 23:32
AlfroJang80AlfroJang80
1483
1483
$begingroup$
Multiply the numerator and the denominator by $(1+z^{-1})^3$ to get the cancellation that you are looking for and multiply it out. Often lecturers will shave some time off the presentation by skipping the tedious steps expecting that students can do the multiplication on their own time. It's likely that what was presented as one step took a few more steps but just weren't shown.
$endgroup$
– Mason
Dec 11 '18 at 23:46
add a comment |
$begingroup$
Multiply the numerator and the denominator by $(1+z^{-1})^3$ to get the cancellation that you are looking for and multiply it out. Often lecturers will shave some time off the presentation by skipping the tedious steps expecting that students can do the multiplication on their own time. It's likely that what was presented as one step took a few more steps but just weren't shown.
$endgroup$
– Mason
Dec 11 '18 at 23:46
$begingroup$
Multiply the numerator and the denominator by $(1+z^{-1})^3$ to get the cancellation that you are looking for and multiply it out. Often lecturers will shave some time off the presentation by skipping the tedious steps expecting that students can do the multiplication on their own time. It's likely that what was presented as one step took a few more steps but just weren't shown.
$endgroup$
– Mason
Dec 11 '18 at 23:46
$begingroup$
Multiply the numerator and the denominator by $(1+z^{-1})^3$ to get the cancellation that you are looking for and multiply it out. Often lecturers will shave some time off the presentation by skipping the tedious steps expecting that students can do the multiplication on their own time. It's likely that what was presented as one step took a few more steps but just weren't shown.
$endgroup$
– Mason
Dec 11 '18 at 23:46
add a comment |
4 Answers
4
active
oldest
votes
$begingroup$
First, multiply (and divide) by $8(1+z^{-1})^3$: you get
$$
frac{8(1+z^{-1})^3}{8(1+z^{-1})^3+8(1+z^{-1})^2(1-z^{-1})+4(1+z^{-1})(1-z^{-1})^2+(1-z^{-1})^3}.
$$
Next, expand the numerator to get
$$
frac{8(1+3z^{-1}+3z^{-2}+z^{-3})}{8(1+z^{-1})^3+8(1+z^{-1})^2(1-z^{-1})+4(1+z^{-1})(1-z^{-1})^2+(1-z^{-1})^3}.
$$
Now, to expand the denominator. Let's do each term:
$$
8(1+z^{-1})^3=8+24z^{-1}+24z^{-2}+8z^{-3};
$$
$$
8(1+z^{-1})^2(1-z^{-1})=8+8z^{-1}-8z^{-2}-8z^{-3};
$$
$$
4(1+z^{-1})(1-z^{-1})^2=4-4z^{-1}-4z^{-2}+4z^{-3};
$$
and
$$
(1-z^{-1})^3=1-3z^{-1}+3z^{-2}-z^{-3}.
$$
Collecting terms, the denominator becomes
$$
(8+8+4+1)+(24+8-4-3)z^{-1}+(24-8-4+3)z^{-2}+(8-8+4-1)z^{-3}
=21+25z^{-1}+15z^{-2}+3z^{-3}.
$$
$endgroup$
$begingroup$
Fantastic. Thank you so much!!!
$endgroup$
– AlfroJang80
Dec 12 '18 at 0:21
add a comment |
$begingroup$
Defining $m:=1-z^{-1}$ and $p:=1+z^{-1}$, we have
$$begin{align}
frac{1}{1+2cdotdfrac12dfrac{m}{p}+2cdotdfrac14dfrac{m^2}{p^2}+dfrac18dfrac{m^3}{p^3}}cdotfrac{8p^3}{8p^3} &= frac{8p^3}{8p^3+8p^2m+4pm^2+m^3} \[2pt]
&=frac{8p^3}{left(2p+mright)left(4p^2+2pm+m^2right)}
end{align}$$
From here, expanding the various pieces is straightforward.
$endgroup$
add a comment |
$begingroup$
I would set $t=z^{-1}$, to get for the denominator:
begin{align}
{}&phantom{={}};1+frac{1-t}{1+t}+frac{(1-t)^2}{2(1+t)^2}+frac{(1-t)^3}{8(1+t)^3}\
&= frac{8(1+t)^3+8(1-t)(1+t)^2+4(1-t)^2(1+t)+(1-t)^3}{8(1+t)^3} \
&= frac{8(1+t)^3+8(1-t^2)(1+t)+4(1-t)(1-t^2)+(1-t)^3}{8(1+t)^3} \
&=dotsm
end{align}
$endgroup$
add a comment |
$begingroup$
Your problem looks very similar to this one.$$frac{1}{t^3+2t^2+2t+1} = frac{1}{t^3+3t^2+3t+1-t^2-t}=frac{1}{(t+1)^3-t(t+1)}=frac{1}{(t+1)(t^2+t+1)}$$
Can you take it from here?
$endgroup$
add a comment |
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4 Answers
4
active
oldest
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4 Answers
4
active
oldest
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$begingroup$
First, multiply (and divide) by $8(1+z^{-1})^3$: you get
$$
frac{8(1+z^{-1})^3}{8(1+z^{-1})^3+8(1+z^{-1})^2(1-z^{-1})+4(1+z^{-1})(1-z^{-1})^2+(1-z^{-1})^3}.
$$
Next, expand the numerator to get
$$
frac{8(1+3z^{-1}+3z^{-2}+z^{-3})}{8(1+z^{-1})^3+8(1+z^{-1})^2(1-z^{-1})+4(1+z^{-1})(1-z^{-1})^2+(1-z^{-1})^3}.
$$
Now, to expand the denominator. Let's do each term:
$$
8(1+z^{-1})^3=8+24z^{-1}+24z^{-2}+8z^{-3};
$$
$$
8(1+z^{-1})^2(1-z^{-1})=8+8z^{-1}-8z^{-2}-8z^{-3};
$$
$$
4(1+z^{-1})(1-z^{-1})^2=4-4z^{-1}-4z^{-2}+4z^{-3};
$$
and
$$
(1-z^{-1})^3=1-3z^{-1}+3z^{-2}-z^{-3}.
$$
Collecting terms, the denominator becomes
$$
(8+8+4+1)+(24+8-4-3)z^{-1}+(24-8-4+3)z^{-2}+(8-8+4-1)z^{-3}
=21+25z^{-1}+15z^{-2}+3z^{-3}.
$$
$endgroup$
$begingroup$
Fantastic. Thank you so much!!!
$endgroup$
– AlfroJang80
Dec 12 '18 at 0:21
add a comment |
$begingroup$
First, multiply (and divide) by $8(1+z^{-1})^3$: you get
$$
frac{8(1+z^{-1})^3}{8(1+z^{-1})^3+8(1+z^{-1})^2(1-z^{-1})+4(1+z^{-1})(1-z^{-1})^2+(1-z^{-1})^3}.
$$
Next, expand the numerator to get
$$
frac{8(1+3z^{-1}+3z^{-2}+z^{-3})}{8(1+z^{-1})^3+8(1+z^{-1})^2(1-z^{-1})+4(1+z^{-1})(1-z^{-1})^2+(1-z^{-1})^3}.
$$
Now, to expand the denominator. Let's do each term:
$$
8(1+z^{-1})^3=8+24z^{-1}+24z^{-2}+8z^{-3};
$$
$$
8(1+z^{-1})^2(1-z^{-1})=8+8z^{-1}-8z^{-2}-8z^{-3};
$$
$$
4(1+z^{-1})(1-z^{-1})^2=4-4z^{-1}-4z^{-2}+4z^{-3};
$$
and
$$
(1-z^{-1})^3=1-3z^{-1}+3z^{-2}-z^{-3}.
$$
Collecting terms, the denominator becomes
$$
(8+8+4+1)+(24+8-4-3)z^{-1}+(24-8-4+3)z^{-2}+(8-8+4-1)z^{-3}
=21+25z^{-1}+15z^{-2}+3z^{-3}.
$$
$endgroup$
$begingroup$
Fantastic. Thank you so much!!!
$endgroup$
– AlfroJang80
Dec 12 '18 at 0:21
add a comment |
$begingroup$
First, multiply (and divide) by $8(1+z^{-1})^3$: you get
$$
frac{8(1+z^{-1})^3}{8(1+z^{-1})^3+8(1+z^{-1})^2(1-z^{-1})+4(1+z^{-1})(1-z^{-1})^2+(1-z^{-1})^3}.
$$
Next, expand the numerator to get
$$
frac{8(1+3z^{-1}+3z^{-2}+z^{-3})}{8(1+z^{-1})^3+8(1+z^{-1})^2(1-z^{-1})+4(1+z^{-1})(1-z^{-1})^2+(1-z^{-1})^3}.
$$
Now, to expand the denominator. Let's do each term:
$$
8(1+z^{-1})^3=8+24z^{-1}+24z^{-2}+8z^{-3};
$$
$$
8(1+z^{-1})^2(1-z^{-1})=8+8z^{-1}-8z^{-2}-8z^{-3};
$$
$$
4(1+z^{-1})(1-z^{-1})^2=4-4z^{-1}-4z^{-2}+4z^{-3};
$$
and
$$
(1-z^{-1})^3=1-3z^{-1}+3z^{-2}-z^{-3}.
$$
Collecting terms, the denominator becomes
$$
(8+8+4+1)+(24+8-4-3)z^{-1}+(24-8-4+3)z^{-2}+(8-8+4-1)z^{-3}
=21+25z^{-1}+15z^{-2}+3z^{-3}.
$$
$endgroup$
First, multiply (and divide) by $8(1+z^{-1})^3$: you get
$$
frac{8(1+z^{-1})^3}{8(1+z^{-1})^3+8(1+z^{-1})^2(1-z^{-1})+4(1+z^{-1})(1-z^{-1})^2+(1-z^{-1})^3}.
$$
Next, expand the numerator to get
$$
frac{8(1+3z^{-1}+3z^{-2}+z^{-3})}{8(1+z^{-1})^3+8(1+z^{-1})^2(1-z^{-1})+4(1+z^{-1})(1-z^{-1})^2+(1-z^{-1})^3}.
$$
Now, to expand the denominator. Let's do each term:
$$
8(1+z^{-1})^3=8+24z^{-1}+24z^{-2}+8z^{-3};
$$
$$
8(1+z^{-1})^2(1-z^{-1})=8+8z^{-1}-8z^{-2}-8z^{-3};
$$
$$
4(1+z^{-1})(1-z^{-1})^2=4-4z^{-1}-4z^{-2}+4z^{-3};
$$
and
$$
(1-z^{-1})^3=1-3z^{-1}+3z^{-2}-z^{-3}.
$$
Collecting terms, the denominator becomes
$$
(8+8+4+1)+(24+8-4-3)z^{-1}+(24-8-4+3)z^{-2}+(8-8+4-1)z^{-3}
=21+25z^{-1}+15z^{-2}+3z^{-3}.
$$
answered Dec 11 '18 at 23:47
Martin ArgeramiMartin Argerami
127k1182182
127k1182182
$begingroup$
Fantastic. Thank you so much!!!
$endgroup$
– AlfroJang80
Dec 12 '18 at 0:21
add a comment |
$begingroup$
Fantastic. Thank you so much!!!
$endgroup$
– AlfroJang80
Dec 12 '18 at 0:21
$begingroup$
Fantastic. Thank you so much!!!
$endgroup$
– AlfroJang80
Dec 12 '18 at 0:21
$begingroup$
Fantastic. Thank you so much!!!
$endgroup$
– AlfroJang80
Dec 12 '18 at 0:21
add a comment |
$begingroup$
Defining $m:=1-z^{-1}$ and $p:=1+z^{-1}$, we have
$$begin{align}
frac{1}{1+2cdotdfrac12dfrac{m}{p}+2cdotdfrac14dfrac{m^2}{p^2}+dfrac18dfrac{m^3}{p^3}}cdotfrac{8p^3}{8p^3} &= frac{8p^3}{8p^3+8p^2m+4pm^2+m^3} \[2pt]
&=frac{8p^3}{left(2p+mright)left(4p^2+2pm+m^2right)}
end{align}$$
From here, expanding the various pieces is straightforward.
$endgroup$
add a comment |
$begingroup$
Defining $m:=1-z^{-1}$ and $p:=1+z^{-1}$, we have
$$begin{align}
frac{1}{1+2cdotdfrac12dfrac{m}{p}+2cdotdfrac14dfrac{m^2}{p^2}+dfrac18dfrac{m^3}{p^3}}cdotfrac{8p^3}{8p^3} &= frac{8p^3}{8p^3+8p^2m+4pm^2+m^3} \[2pt]
&=frac{8p^3}{left(2p+mright)left(4p^2+2pm+m^2right)}
end{align}$$
From here, expanding the various pieces is straightforward.
$endgroup$
add a comment |
$begingroup$
Defining $m:=1-z^{-1}$ and $p:=1+z^{-1}$, we have
$$begin{align}
frac{1}{1+2cdotdfrac12dfrac{m}{p}+2cdotdfrac14dfrac{m^2}{p^2}+dfrac18dfrac{m^3}{p^3}}cdotfrac{8p^3}{8p^3} &= frac{8p^3}{8p^3+8p^2m+4pm^2+m^3} \[2pt]
&=frac{8p^3}{left(2p+mright)left(4p^2+2pm+m^2right)}
end{align}$$
From here, expanding the various pieces is straightforward.
$endgroup$
Defining $m:=1-z^{-1}$ and $p:=1+z^{-1}$, we have
$$begin{align}
frac{1}{1+2cdotdfrac12dfrac{m}{p}+2cdotdfrac14dfrac{m^2}{p^2}+dfrac18dfrac{m^3}{p^3}}cdotfrac{8p^3}{8p^3} &= frac{8p^3}{8p^3+8p^2m+4pm^2+m^3} \[2pt]
&=frac{8p^3}{left(2p+mright)left(4p^2+2pm+m^2right)}
end{align}$$
From here, expanding the various pieces is straightforward.
answered Dec 11 '18 at 23:47
BlueBlue
48.4k870154
48.4k870154
add a comment |
add a comment |
$begingroup$
I would set $t=z^{-1}$, to get for the denominator:
begin{align}
{}&phantom{={}};1+frac{1-t}{1+t}+frac{(1-t)^2}{2(1+t)^2}+frac{(1-t)^3}{8(1+t)^3}\
&= frac{8(1+t)^3+8(1-t)(1+t)^2+4(1-t)^2(1+t)+(1-t)^3}{8(1+t)^3} \
&= frac{8(1+t)^3+8(1-t^2)(1+t)+4(1-t)(1-t^2)+(1-t)^3}{8(1+t)^3} \
&=dotsm
end{align}
$endgroup$
add a comment |
$begingroup$
I would set $t=z^{-1}$, to get for the denominator:
begin{align}
{}&phantom{={}};1+frac{1-t}{1+t}+frac{(1-t)^2}{2(1+t)^2}+frac{(1-t)^3}{8(1+t)^3}\
&= frac{8(1+t)^3+8(1-t)(1+t)^2+4(1-t)^2(1+t)+(1-t)^3}{8(1+t)^3} \
&= frac{8(1+t)^3+8(1-t^2)(1+t)+4(1-t)(1-t^2)+(1-t)^3}{8(1+t)^3} \
&=dotsm
end{align}
$endgroup$
add a comment |
$begingroup$
I would set $t=z^{-1}$, to get for the denominator:
begin{align}
{}&phantom{={}};1+frac{1-t}{1+t}+frac{(1-t)^2}{2(1+t)^2}+frac{(1-t)^3}{8(1+t)^3}\
&= frac{8(1+t)^3+8(1-t)(1+t)^2+4(1-t)^2(1+t)+(1-t)^3}{8(1+t)^3} \
&= frac{8(1+t)^3+8(1-t^2)(1+t)+4(1-t)(1-t^2)+(1-t)^3}{8(1+t)^3} \
&=dotsm
end{align}
$endgroup$
I would set $t=z^{-1}$, to get for the denominator:
begin{align}
{}&phantom{={}};1+frac{1-t}{1+t}+frac{(1-t)^2}{2(1+t)^2}+frac{(1-t)^3}{8(1+t)^3}\
&= frac{8(1+t)^3+8(1-t)(1+t)^2+4(1-t)^2(1+t)+(1-t)^3}{8(1+t)^3} \
&= frac{8(1+t)^3+8(1-t^2)(1+t)+4(1-t)(1-t^2)+(1-t)^3}{8(1+t)^3} \
&=dotsm
end{align}
answered Dec 12 '18 at 0:06
BernardBernard
121k740116
121k740116
add a comment |
add a comment |
$begingroup$
Your problem looks very similar to this one.$$frac{1}{t^3+2t^2+2t+1} = frac{1}{t^3+3t^2+3t+1-t^2-t}=frac{1}{(t+1)^3-t(t+1)}=frac{1}{(t+1)(t^2+t+1)}$$
Can you take it from here?
$endgroup$
add a comment |
$begingroup$
Your problem looks very similar to this one.$$frac{1}{t^3+2t^2+2t+1} = frac{1}{t^3+3t^2+3t+1-t^2-t}=frac{1}{(t+1)^3-t(t+1)}=frac{1}{(t+1)(t^2+t+1)}$$
Can you take it from here?
$endgroup$
add a comment |
$begingroup$
Your problem looks very similar to this one.$$frac{1}{t^3+2t^2+2t+1} = frac{1}{t^3+3t^2+3t+1-t^2-t}=frac{1}{(t+1)^3-t(t+1)}=frac{1}{(t+1)(t^2+t+1)}$$
Can you take it from here?
$endgroup$
Your problem looks very similar to this one.$$frac{1}{t^3+2t^2+2t+1} = frac{1}{t^3+3t^2+3t+1-t^2-t}=frac{1}{(t+1)^3-t(t+1)}=frac{1}{(t+1)(t^2+t+1)}$$
Can you take it from here?
answered Dec 13 '18 at 1:04
John JoyJohn Joy
6,29111627
6,29111627
add a comment |
add a comment |
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$begingroup$
Multiply the numerator and the denominator by $(1+z^{-1})^3$ to get the cancellation that you are looking for and multiply it out. Often lecturers will shave some time off the presentation by skipping the tedious steps expecting that students can do the multiplication on their own time. It's likely that what was presented as one step took a few more steps but just weren't shown.
$endgroup$
– Mason
Dec 11 '18 at 23:46