Q:

# What is the formula for the Law of Cosines?

A:

The formula for the law of cosines is c^2 = a^2 + b^2 - 2ab x cos(C), where a, b and c are the sides of a triangle, and C is the angle opposite side c. The law of cosines is derived from the Pythagorean theorem.

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The law of cosines can be used to find the angles of a triangle when only given the lengths of each side. It can also be used to the find the length of a side when given the lengths of two sides and the size of the angle opposite the unknown side. For example, for the triangle where a = 9, b = 5 and c = 8, the value of c is calculated as 62.2 degrees.

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