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