Practice!

Sample Problem

Find the exact value of sin(-15°).

Solution

-15° is coterminal with 345°=300°+45°

Use the sum and difference formula.

sin(345°)=sin(300°+45°)

=sin(300°)cos(45°)+cos(300°)sin(45°)

=(-√3/2)(√2/2)+(1/2)(√2/2)

=(-√3/2√2)+(1/2√2)

=(-√3+1/2√2)