Sum and Difference Identities

	$\displaystyle \sin(x\pm y)=\sin x \cos y\pm \cos x \sin y$
	$\displaystyle \cos(x\pm y)=\cos x \cos y\mp \sin x \sin y$
	$\displaystyle \tan(x\pm y)=\frac{\tan x\pm \tan y}{1\mp \tan x \tan y}$