write 2(sin^2(x)- cos^2(x)) + 6 sin(x) cos(x) in terms of cos(2x) and sin(2x)
We use the following double angle formulae cos(2x) = cos^2(x) - sin^2 (x) and sin(2x) = 2sin(x)cos(x) to see that 2(sin^2(x)- cos^2(x)) + 6 sin(x) cos(x) = -2-(sin^2(x)+ cos^2(x)) + 3*2 sin(x) cos(x) = -2cos(2x) + 3sin(2x)