Question

The law of sines and the law of cosines both provide a way to solve a triangle given three pieces of information about the sides and angles (other than being given three angles). In what two scenarios must you begin solving the triangle by using the law of cosines?

Answer 1

Explanation:

I call the law of cosine the extended Pythagoras for general triangles (not just right-angled).

c² = a² + b² - 2ab×cos(C)

with C being the angle opposite of the side C.

we can use this, when we know all 3 side lengths and need to know the angles.

and we can use this when we know 2 sides and their enclosed angle to get the third side length.