Trigonometry Examples

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

Step 1

Start on the left side.

$\sin^{2} (x) - \cos^{2} (x)$

Step 2

Apply Pythagorean identity in reverse.

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

Step 3

Subtract ${\cos (x)}^{2}$ from $- {\cos (x)}^{2}$ .

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

Step 4

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

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