How to find an angle of triangle that is not right angled when two sides are given

The Law of Cosines (also called the Cosine Rule) says:

c^2 = a^2 + b^2 - 2ab cos (C)

The Law of Cosines is useful for finding:

the third side of a triangle when we know two sides and the angle between them

the angles of a triangle when we know all three sides

The Law of Sines (or Sine Rule) is very useful for solving triangles:

a/sin A = b/sin B = c/sin C

a, b and c are sides.

A, B and C are angles.

(Side a faces angle A,

side b faces angle B and

side c faces angle C).

When we divide side a by the sine of angle A

it is equal to side b divided by the sine of angle B,

and also equal to side c divided by the sine of angle C