The Sine & Cosine Rules

For triangles that are not right-angled, use the sine and cosine rules. Sides $a,b,c$ are opposite angles $A,B,C$.

The sine rule

$$\frac{a}{\sin A}=\frac{b}{\sin B}=\frac{c}{\sin C}$$ Use when you have a side and its opposite angle, plus one more side or angle. (To find an angle, flip it: $\frac{\sin A}{a}=\frac{\sin B}{b}$.)