(New page: Category:2010 Fall ECE 438 Boutin == Solution to Q4 of Week 5 Quiz Pool == ---- From the first question, we knew that <math> -a^{n}u[-n-1] = \mathcal{Z}^{-1}\bigg\{\frac{1}{1-az^{-...)
 
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From the first question, we knew that  
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From the definition, we know that
  
<math> -a^{n}u[-n-1] = \mathcal{Z}^{-1}\bigg\{\frac{1}{1-az^{-1}}\bigg\} \text{ where } |z|<|a|. \,\!</math>
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<math> H(e^{jw}) = \frac{e^{jw}-j}{e^{jw}-2} \,\!</math>
  
And the time-shifting property of Z-transform is defined as
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<math> \text{For } w_1, \; |H(e^{j w_1})| = \bigg|\frac{e^{j\frac{\pi}{2}}-j}{e^{j\frac{\pi}{2}}-2}\bigg| = 0, \;\; \text{ since } e^{j\frac{\pi}{2}}=j. \,\!</math>
  
<math> x[n-k] = \mathcal{Z}^{-1}\bigg\{z^{-k}X(z)\bigg\} \text{   when  } x[n] = \mathcal{Z}^{-1}\bigg\{X(z)\bigg\}\,\!</math>
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<math> \text{For } w_2, \; \text{ since } e^{-j\frac{\pi}{2}}=-j, \; H(e^{j w_2}) = \frac{e^{-j\frac{\pi}{2}}-j}{e^{-j\frac{\pi}{2}}-2} = \frac{-j-j}{-j-2} = \frac{2j}{2+j}.  \,\!</math>
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Therefore,
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<math> |H(e^{j w_2})| = \bigg|\frac{2j}{2+j}\bigg| = \frac{2}{\sqrt{5}}. \,\!</math>
  
Therefore, if we use the time-shifting property of Z-transform, then
 
  
<math> -a^{n-3}u[-(n-3)-1] = \mathcal{Z}^{-1}\bigg\{\frac{z^{-3}}{1-az^{-1}}\bigg\} \text{ where } |z|<|a|. \,\!</math>
 
  
Combined with the result from the linearity of Z-transform, then
 
  
<math>
 
\begin{align}
 
\mathcal{Z}^{-1}\bigg\{\frac{2z^{-3}}{1-az^{-1}}\bigg\}  \text{ for } |z|<|a| &= -2a^{n-3}u[-(n-3)-1], \\
 
&= -2a^{n-3}u[-n+2]
 
\end{align}
 
\,\!</math>
 
 
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Revision as of 15:13, 19 September 2010


Solution to Q4 of Week 5 Quiz Pool


From the definition, we know that

$ H(e^{jw}) = \frac{e^{jw}-j}{e^{jw}-2} \,\! $

$ \text{For } w_1, \; |H(e^{j w_1})| = \bigg|\frac{e^{j\frac{\pi}{2}}-j}{e^{j\frac{\pi}{2}}-2}\bigg| = 0, \;\; \text{ since } e^{j\frac{\pi}{2}}=j. \,\! $

$ \text{For } w_2, \; \text{ since } e^{-j\frac{\pi}{2}}=-j, \; H(e^{j w_2}) = \frac{e^{-j\frac{\pi}{2}}-j}{e^{-j\frac{\pi}{2}}-2} = \frac{-j-j}{-j-2} = \frac{2j}{2+j}. \,\! $

Therefore,

$ |H(e^{j w_2})| = \bigg|\frac{2j}{2+j}\bigg| = \frac{2}{\sqrt{5}}. \,\! $




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