show $\displaystyle tan^{-1}(\frac{2x}{x^{2}+y^{2}-1}) $ is harmonic by considering $\displaystyle h(w(z))=log(\frac{i+z}{i-z}) $

i found that h(w(z)) is just the same as the function required. but how can i show it is harmonic by writing it as composition of maps?