Question

Law of cosine formula​

Answer 1

The cosine of a right angle is 0, so the law of cosines, c2 = a2 + b2 – 2ab cos C, simplifies to becomes the Pythagorean identity, c2 = a2 + b2, for right triangles which we know is valid.

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Answer 2

It can be in either of these forms:

• cos(C) = a2 + b2 − c2 2ab.
• cos(A) = b2 + c2 − a2 2bc.
• cos(B) = c2 + a2 − b2 2ca.