Cosines, Law of

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Cosines, Law of


a law of trigonometry asserting that the square of a side of a triangle is equal to the sum of the squares of the other two sides less twice the product of these sides by the cosine of the angle between them:

c2 = a2 + b2—2 ab cos α

Here, a, b, and c are the sides of the triangle and α is the angle between sides a and b.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.