Question

Express cos^2 x in terms of cos2x. Hence, express f(x) = 6cos^2 x - 4sin 2x in the form R cos (2x + Y degrees) + p where R, y and p are constants. Find the maxium and minimum values of f(x) and sketch its graph in the domain -180 <= x <= 360

Answer 1

2cos^2 x = 1 + cos 2x
cos^2 x = 1/2(1 + cos 2x)
f(x) = 6cos^2 x - 4 sin 2x = 6(1/2(1 + cos 2x) - 4 sin 2x = 3 + 3cos 2x - 4sin 2x