Identidades trigonométricas

Mnemotécnicas

SOR: Seno = Ordenada (y) / Radio
CAR: Coseno = Abscisa (x) / Radio
TOA: Tangente = Ordenada / Abscisa = y/x

$\cos (x) - \cos (- x) = 0$
$\sin (x)^{2} + \cos (x)^{2} = 1$
$\cos^{2} (x) - \sin^{2} (x) = \cos (2 x)$
$\sin (x) - \sin (- x) = 2 \sin (x)$
$\cos (x + y) = \cos x \cdot \cos y - \sin x \cdot \sin y$

Límites

$lim_{x \to 0} \frac{\sin (x)}{x} = 1$
$lim_{(x, y) \to (0, 0)} \frac{\sin (x y)}{x y} = 1$