Question

Write the expression as either the sine, cosine, or tangent of a single angle.

Answer 1

we know that cos(a - b) = cos(a) cos(b) + sin(a) sin(b)
given a = π/3 and b = π/5
cos(π/3) cos(π/5) + sin(π/3) sin(π/5) = cos((π/3) - (π/5) = cos(2π/15)
hope it helps