The integral ∮ f (z) dz evaluated around the unit

The integral ∮ f (z) dz evaluated around the unit circle on the complex plane for f(z) = cosz/z is

f(z) =	cosz	has simple pole at z = 0
	z

∴ Residue of f (z) at z = 0
Ltf (z) = Lt cos z = 1
z → 0 z → 0
= 2 π i (Residue at z = 0)