Question

Помогите!
Cos п/5*cos п/8=?
Sin п/10*cos п/8=?

Answer 1

Cos п/5*cos п/8=1/2сos(π/5-π/8)+1/2cos(π/5+π/8)=
=1/2cos3π/40+1/2cos13π/4
Sin п/10*cos п/8=1/2sin(π/5-π/8)+1/2sin(π/5+π/8)=
=1/2sin3π/40+1/2sin13π/4