# is there a formula for working out the angles of a triangle to make the sides meet at the top?

I am doing a GCSE maths foundation paper for revision and one question has a triangle with the base side being 9cm and the other 2 sides 7.5cm. Is there a formula for finding the angles of the triangle given the lengths of each side so that the 2 side lengths join together at the top to complete the triangle?

Thanks

$$\cos A=\frac{7.5^2+7.5^2-9^2}{2\cdot7.5\cdot 7.5}$$