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
