Question

How we come to know when to use sine rule and when to use cosine rule

Answer 1

Sine and Cosine Rule

This section looks at the Sine Law and Cosine Law.

The Sine Rule

The Law of Sines (sine rule) is an important rule relating the sides and angles of any triangle (it doesn't have to be right-angled!):

If a, b and c are the lengths of the sides opposite the angles A, B and C in a triangle, then:

 a   =   b  =  c 

sinA    sinB  sinC

If you wanted to find an angle, you can write this as:

sinA =  sinB  = sinC