Question

prove this identity 3cos2x=2-sinx

Answer 1

there is something wrong!
the right hand side shouldn't be that way

Answer 2

hmm 3cos2x=3(1-2sin^2x)=3-6sin^2x

Answer 3

if you try half angle identity it won't give that result as well

Answer 4

RHS does not equal the lLHS