Question

cos3x+cos7x=1+cos10x

Answer 1

2cos5xcos2x-2cos²5x=0
2cos5x(cos2x-1)=0
cos5x=0⇒5x=π/2+πn⇒x=π/10+πn/5
cos2x=1⇒2x=2πn⇒x=πn