Question

If 3 cos x + 2 cos 3x = cos y, 3 sin x + 2 sin 3x = sin y, then the value of cos 2x is​

Answer 1

Step-by-step explanation:

3cosx + 2cos 3x = cos y ----- eq1

3 since + 2 sin3x = Sony ---- eq2

9 cos^2x + 4 cos^2 3x + 12 coax. cox3x + 9 sin^2x + 4 sin^2 3x +12 sinx. sin3x= cos ^2y+ sin^2y

9+4+12(cosx.cos3x + sinx. sin3x) =1

12( cos (x-3x)) =-12

cos 2x = -1