The law of sines is an equation that relates the three sides of a triangle with the three angles of a triangle using the sine function.

This example derives the law of sines by dividing the general case of the triangle into two right triangles, applying the definition of sine to the share opposite side and equating the expressions together.

The law of sines can be derived using a triangle inscribed on the perimeter of a circle. The proof uses the inscribed angle theorem.