Cosine Theorem

Online calculator provides the ability to easily and accurately calculate the length of one of the sides of a triangle using the Cosine Theorem - knowing two sides and the angle.

Cosine Theorem — is a geometric theorem that relates the lengths of the sides of a triangle to the cosines of its angles. In a triangle with sides a, b and c and angles α, β and γ respectively, the cosine theorem states the following:

c² = a² + b² - 2ab * cos(γ)
b² = a² + c² - 2ac * cos(β)
a² = b² + c² - 2bc * cos(α)

This theorem allows calculating the length of one of the sides of a triangle if the lengths of the other two sides and the measure of the angle between them are known. The cosine theorem is important in geometry and in solving various problems related to triangles.