Law of Cosines

The Law of Sines is used to solve triangles when we are given two sides and a non-included angle.

If we are given two sides and an included angle or three sides then we can use the Law of Cosines to solve the triangle.

The Law of Cosines, for any triangle ABC is

a ² = b ² + c ² – 2bc cos A

b ² = a ² + c ² – 2ac cos B

c ² = a ² + b ² – 2ab cos C

We can use the Law of Cosines and the Law pf Sines when solving triangles. Solving a triangle means to find the unknown lengths and angles of the triangle.

The following video shows examples of solving triangles using Law of Cosines.

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