M7 · Expert
Trigonometry
Sine and cosine rules
Formula
a/sin A = b/sin B ; c^2 = a^2 + b^2 - 2ab cos C
Rule
Use the sine rule for pairs of side and angle, the cosine rule for three sides or two sides and the included angle.
Example
With two sides and the included angle, use the cosine rule.
Tip
Right triangles need SOH CAH TOA, others need these rules.
Learn this concept
Trigonometry