Cos (7п/5-a) cos(2п/5+а)+sin(7п/5-a) sin(2п/5+а)

Question

Cos (7п/5-a) cos(2п/5+а)+sin(7п/5-a) sin(2п/5+а)

Answer 1

Формулы для решения: sinX*sinY=1/2(cos(X-Y)-cos(X+Y)). cosX*cosY=1/2(cos(X+Y)+cos(X-Y))