cos

$$\sin(2\theta) = 2 \cdot \sin(\theta) \cdot \cos(\theta)$$

$$\scriptsize \sin(a \pm b) = \sin(a) \cos(b) \pm \cos(a) \sin(b)$$

$$c^2 = a^2 + b^2 - 2 \cdot a \cdot b \cdot \cos(\theta)$$