1. Exercise #16
Sum and Difference Identities I
Sum Formulae
sin( ) sin cos sin cos
cos( ) cos cos sin sin
Difference Formulae
sin( ) sin cos sin cos
cos( ) cos cos sin sin
We can use the formulae to find exact values that are not covered with the special
triangles.
Example
7
Evaluate sin .
12
Example
Find the exact value of cos195 .
2. Try
Find the exact value of sin .
12
Example
4 12 3
If cos where and cos where , find cos( ) .
5 2 13 2
3. Try
3 3 40 3
Given sin where 2 and cos where 2 , find cos( ) .
5 2 41 2