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Evaluate $\oint_c \frac{e^{2z}}{ (z+1)^4} dz$ where C is the circle |z-1|=3
1 Answer
written 5.0 years ago by | • modified 5.0 years ago |
Solution:
Given, $\oint_c \frac{e^{2z}}{ (z+1)^4} dz$
$z=-1 \ is \ a \ pole \ of \ order \ 4 \ i.e.m=4$
$residue \ of \ f(z) \ at \ z=-1$
$\frac{1}{(m-1)!}\lim_{z \to z_0} \frac{d^{m-1}}{dz^{m-1}}[(z-z_0)^{m} f(z)]$
$\frac{1}{(4-1)!}\lim_{z \to -1} \frac{d^{4-1}}{dz^{4-1}}[(z+1)^{4} \frac{e^{2z}}{ {(z+1)}^4} ]$
$\frac{1}{(3)!}\lim_{z \to -1} \frac{d^{3}}{dz^{3}}[e^{2z} ]$
$\frac{1}{6}[e^{2z} 8]$
=$\frac{8}{6}[e^{-2}]$
=$\frac{4}{3}[e^{-2}]$
$\oint_c \frac{e^{2z}}{ (z+1)^4} dz$ = $2\pi i f(z)$
$=2\pi i \frac {4}{3}e^{-2}$
$\oint_c \frac{e^{2z}}{ (z+1)^4} dz$=$\pi i \frac {8}{3}e^{-2}$