Trigonometry Examples

$\cos (2 a) = 2 \cos^{2} (a) - 1$

Step 1

Start on the right side.

$2 \cos^{2} (a) - 1$

Step 2

Apply the cosine double-angle identity.

$\cos (2 a)$

Step 3

Because the two sides have been shown to be equivalent, the equation is an identity.

$\cos (2 a) = 2 \cos^{2} (a) - 1$ is an identity