Question

Question #7d8c7

Answer 1

`LHS=cos6x`

`=cos(3x+3x)`

`=cos3xcos3x-sin3xsin3x`

`=cos^2 3x-sin^2 3x`

`=cos^2 3x-(1-cos^2 3x)`

`=cos^2 3x-1+cos^2 3x)`

`=2cos^2 3x-1=RHS`

Proved