Express cos(2x) in the form acos^2(x) + b, where a and b are constants.

we first remember the double angle formula, a really important formula. cos(2x) = cos²(x) - sin²(x).We know that sin²(x) + cos²(x) = 1, therefore, cos(2x) = cos²(x) + cos²(x) - 1. Giving our final answer to be, cos(2x) = 2cos²(x) - 1.