Write the expression as the sine, cosine, or tangent of an angle

Problem: cos (pi/2) cos(pi/7) + sin(pi/2) sin(pi/7)

I start with the cos(u - v) = cos( pi/2 - pi/7) =

(90 degrees - 25.7) < turned radians into degrees [pi/7 (180/pi)]=about 25.7

=

cos(64.3) = .433