The Cosine Rule

We can use the cosine rule to:


1. Find a side when it is opposite a known angle and that angle is between two known sides.

We start by labelling the sides a,b,c and the angles A,B,C with sides opposite their respective angles as shown.


2 Find an angle when all three sides are known.

We start by labelling the sides a,b,c and the angles A,B,C with sides opposite their respective angles as shown.