Question

How your verify `1/8[3+4cos2x+cos4x]=cos^ 4x`?

Answer 1

`RHS=cos^4x`

`=[(2cos^2x)/2]^2`

`=1/4[1+cos2x]^2`

`=2/(4*2)[1+2cos2x+cos^2(2x)]`

`=1/8[2+4cos2x+2cos^2(2x)]`

`=1/8[2+4cos2x+1+cos4x]=1/8[3+4cos2x+cos4x]=LHS`