cos 6х+cos 8х=cos10 х+cos 12х

Question

cos 6х+cos 8х=cos10 х+cos 12х

Answer 1

Cos6x+cos8x=cos10x+cos12x

2cos7xcosx=2cos11xcosx

cosx(cos7x-cos11x)=0

cosx=0  или cos7x=cos11x

x=П/2+Пn.    2sin9xsin2x=0

                      X=Пn/9x=Пn/2