Law of Cosines

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The law of cosines is a formula related to SAS congruence.
It shows how to compute a side c once one knows the sides a and b and the included angle C.

c2= a2 + b2 - 2ab cos C

This law is a generalization of the Pythagorean Theorem. When angle C is a right angle and thus cos C = 0, the formulas is the same as the Pythagorean Thereom.

The Law of Cosines is what permits the computation of the cosine of an angle by dot product of vectors.


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