If z=cosθ+isinθz = \cos\theta + i\sin\thetaz=cosθ+isinθ, what is 1+z1−z\frac{1+z}{1-z}1−z1+z?
icot(θ/2)i\cot(\theta/2)icot(θ/2)
−icot(θ/2)-i\cot(\theta/2)−icot(θ/2)
itan(θ/2)i\tan(\theta/2)itan(θ/2)
cot(θ/2)\cot(\theta/2)cot(θ/2)