①SOH CAH TOA
$\sin=\tfrac{O}{H}$ $\cos=\tfrac{A}{H}$ $\tan=\tfrac{O}{A}$ · angle: use $\sin^{-1}/\cos^{-1}/\tan^{-1}$
②SIDES
$x$ on top: multiply. $x$ on bottom: $x=\dfrac{\text{side}}{\text{ratio}}$ · 3rd side: $H^2=O^2+A^2$
③ELEV / DEPR
Elevation = look up · Depression = look down · they’re equal (alternate angles)
④SINE RULE
$\dfrac{a}{\sin A}=\dfrac{b}{\sin B}$ · angle → flip: $\dfrac{\sin A}{a}=\dfrac{\sin B}{b}$
⑤COSINE RULE
$a^2=b^2+c^2-2bc\cos A$ · two sides + angle between, or three sides
⑥AREA
$\text{Area}=\tfrac{1}{2}ab\sin C$ · square units · find the in-between angle first if needed