1. Can you use the sine rule with right- angled triangles?

No, not really. It works but it is a harder way and it takes much longer.

2. What is the most common mistake made by people using the cosine rule?

They put the numbers for a, b and c in the wrong places.

2. How do you decide whether to use the SINE rule or the COSINE rule?

Look for pairs of angles and sides. If you can find 2 pairs of these (including the variable) you use the sine rule.

Always use the cosine rule when you are given THREE sides and need to find one or more of the angles OR when you are given two sides and the angle between them.