Question

Which identity is used for an even power of cosine?

Options

• \(\cos^2 x = \frac{1+\cos 2x}{2}\)

• \(\cos 2x = 2\cos^2 x+1\)

• \(\cos^2 x = 1+\cos 2x\)

• \(\sin^2 x = \frac{1+\cos 2x}{2}\)

Answer 1

For an even power of cosine, use \(\cos^2 x = \frac{1+\cos 2x}{2}\). This changes the power into a constant term and a cosine term.