Topics · 4 identities

Basics

The core ratios, degree–radian conversion, and circle measures every trig course opens with.

SOHCAHTOA

\sin\theta = \dfrac{\text{opp}}{\text{hyp}}\quad \cos\theta = \dfrac{\text{adj}}{\text{hyp}}\quad \tan\theta = \dfrac{\text{opp}}{\text{adj}}

Mnemonic for the three core ratios in a right triangle.

1^{\circ} = \dfrac{\pi}{180}\text{ rad}\qquad 1\text{ rad} = \dfrac{180}{\pi}^{\!\!\circ}

s = r\theta

θ must be in radians.

A = \tfrac{1}{2} r^{2} \theta

θ in radians.