sin3x =sin(x)*( 3cos^2 x - sin^2 x )
sin3x =
sin (2x + x) =
sin2xcosx + cos2xsinx =
(2sinxcosx)cosx + (cos^2x - sin^2x)sinx =
2sinxcos^2x + sinxcos^2x - sin^3x =
3sinxcos^2x - sin^3x =
sinx*(3cos^2x - sin^2x) ......and this equals the right hand side......
Prove that the equation is an identity.
