Make the substitution:z=eiθ,dz=ieiθdθ. Now the complex z describes the unit circle C1 in the positive sense as θ varies from to 2π.
The integral becomes
∫02π2+sinθdθ=∮C12+2izz2−1izdz
=∮C1z2+4iz−12dz The poles of the integrand are simple and occur when z2+4iz−1=0
z±=2−4i±−16+4=(−2±3)i
z+z−=(−2+3)i(−2−3)i=−1Therefore, z+ is a (simple) pole inside the unit circle.
Use Resz=z0h(z)g(z)=h′(z0)g(z0), where z0 is a simple zero of h(z).
Then
Res(z+)=2z++4i2=−2i+3i+2i1=3i1 Thus, by the residue theorem,
∫02π2+sinθdθ=2πi(3i1)=32π
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