Question

cos 12x *cos7x-cos4x*cos15x=0

Answer 1

12(соs5x-cos19x)-12(cos9x-cos19x)=0 12cos 5x -12cos19x-12cos9x+12cos19x=0 Cos 5x - cos 9x =0 -2 sin 7x sin 2 x=0 Sin 7 x = 0 Sin 2 x= 0 X=PN7 x=pn/2