# How do you solve tan(x+ y) = (tan x + tan y) / (1 - tan x tan y)?

It is a trignometrical identity, there is nothing there to solve. The identity is arrived at by simplifying the identities in $\sin \frac{x + y}{\cos} \left(x + y\right)$
= $\frac{\sin x \cos y + \cos x \sin y}{\cos x \cos y - \sin x \sin y}$.
$\frac{\tan x + \tan y}{1 - \tan x \tan y}$