Cos 5π/8*Cos 3π/8+Sin 5π/8*Sin 3π/8

Question

Cos 5π/8*Cos 3π/8+Sin 5π/8*Sin 3π/8

Answer 1

cos(5П/8)*cos(3П/8)+sin(5П/8)*sin(3П/8)=cos(5π/8-3π/8)=cos(2π/8)=cos(π/4)=1/√2