Chapter D, Problem 40E

$\left(a\right)$

To determine

To Prove: the equation $\tan \left(x+y\right)=\frac{\tan x+\tan y}{1-\tan x\tan y}$ .

  $\left(b\right)$

To determine

To Prove: the equation $\tan \left(x-y\right)=\frac{\tan x-\tan y}{1+\tan x\tan y}$ .