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Find the residues of the following functions at the indicated points. Try to select the easiest of the methods outlined above. Check your results by computer.

e2z4coshz-5atz=ln2

Short Answer

Expert verified

The residue of the function at z=ln2is R(ln2)=43

Step by step solution

01

Determine the formula 

Simple pole at the residue is given by the function as:

R[f(z)]=limz→z0(z-z0)f(z)

02

Determine the residue of the simple pole

Consider the given function as:

f(z)=e2z4coshz-5

Rewrite the function as:

f(z)=q(z)p(z)=e2z4coshz-5 …… (1)

At z=ln2

The function has simple pole at z=ln2and the residue of simple pole is given by:

R(z0)=limz→z0(z-z0)f(z)=q(z0)p(z0) ……. (2)

03

 Determine the residue of the function as:

Substitute the values in equation (2) as follows:

R(ln2)=e2ln24sinh(ln2)=1sinh(ln2)=43

Therefore, the residue of a function at z=ln2is R(ln2)=43.

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