Practice!

Sample Problem

Write cos(π/19)sin(4π/19)-sin(π/19)cos(4π/19) as the sine, cosine, or tangent of an angle.

Solution

cos(π/19)sin(4π/19)-sin(π/19)cos(4π/19)

=sin(4π/19)cos(π/19)-cos(4π/19)sin(π/19)

=sin(4π/19-π/19)

=sin(3π/19)