Cosine Rule

🎬 Video Tutorial

(0:01) Cosine Rule: Use it to find missing sides or angles in non-right-angled triangles.
(0:13) Cosine Rule Formula: For any triangle, the formula is: $a^2 = b^2 + c^2 – 2bc \cdot \cos(A)$, where $A$ is the angle opposite side $a$.
(0:28) Finding a Missing Side: If two sides and the included angle are known, plug values into the Cosine Rule to solve for the third side.
(1:57) Finding an Angle with the Cosine Rule: Rearrange the formula to find the cosine of an angle when all three sides are known.