Sine Rule & Cosine Rule
Use these for non-right-angled triangles.
\(\frac{a}{\sin A} = \frac{b}{\sin B} = \frac{c}{\sin C}\)
\(c^2 = a^2 + b^2 - 2ab\cos C\)
\(\text{Area} = \frac{1}{2}ab\sin C\)
Sine Rule: 2 angles + 1 side or 2 sides + non-included angle.
Cosine Rule: 2 sides + included angle or all 3 sides.
Example
Example: In triangle ABC, given a = 8, b = 6, angle C = 60°, use Cosine Rule to find side c.
Practice
Lvl 2
Which formula is the Cosine Rule?
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