Question #292044

f(z)= z/(z+1)(z+1)^2

1
Expert's answer
2022-01-31T16:52:42-0500

The form of the partial fraction decomposition is;

z(z+1)3=Az+1+B(z+1)2+C(z+1)3=z(z+1)3=(z+1)2A+(z+1)B+C(z+1)3z=(z+1)2A+(z+1)B+C\displaystyle \frac{z}{\left(z + 1\right)^{3}}=\frac{A}{z + 1}+\frac{B}{\left(z + 1\right)^{2}}+\frac{C}{\left(z + 1\right)^{3}}=\frac{z}{\left(z + 1\right)^{3}}=\frac{\left(z + 1\right)^{2} A + \left(z + 1\right) B + C}{\left(z + 1\right)^{3}}\\ \Rightarrow z=\left(z + 1\right)^{2} A + \left(z + 1\right) B + C\\

Expanding the right hand side yields;

z=z2A+2zA+zB+A+B+CCollecting like terms yields;z=z2A+z(2A+B)+A+B+CComparing yields the following system of linear equations:{A=02A+B=1A+B+C=0Solving the above equations yields: A=0, B=1, C=1z(z+1)3=0z+1+1(z+1)2+1(z+1)3=z(z+1)3=1(z+1)21(z+1)3\displaystyle z=z^{2} A + 2 z A + z B + A + B + C\\ \text{Collecting like terms yields;}\\ z=z^{2} A + z \left(2 A + B\right) + A + B + C\\ \text{Comparing yields the following system of linear equations:}\\ \qquad\qquad\qquad\qquad\qquad\qquad\qquad\begin{cases} A = 0\\2 A + B = 1\\A + B + C = 0 \end{cases}\\ \text{Solving the above equations yields: }A=0,\ B=1,\ C=-1\\ \therefore\frac{z}{\left(z + 1\right)^{3}}=\frac{0}{z + 1}+\frac{1}{\left(z + 1\right)^{2}}+\frac{-1}{\left(z + 1\right)^{3}}=\frac{z}{\left(z + 1\right)^{3}}=\frac{1}{\left(z + 1\right)^{2}}-\frac{1}{\left(z + 1\right)^{3}}


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