Here is a step-by-step derivation:
(E^(I v) - 1)/(E^(I v) + 1) ==
(1 + x)/(1 - x)*(Exp[I E] - 1)/(Exp[I E] + 1)
MultiplySides[%, E^(I v) + 1, GenerateConditions -> False]
Collect[%, E^(I v)]
AddSides[%, 1 - %[[2, 2]]]
Collect[%, E^(I v), Factor]
DivideSides[%, %[[1]]/E^(I v), GenerateConditions -> False]