Chapter D, Problem 40E

(a)

To determine

To prove: The equation $\tan \left(x+y\right)=\frac{\tan x+\tan y}{1-\tan x\mathrm{tany}}$.

(b)

To determine

To prove: The equation $\tan \left(x-y\right)=\frac{\tan x-\tan y}{1+\tan x\mathrm{tany}}$.