Algebra Examples

$\cos^{2} (135 °) - \sin^{2} (135 °)$

Step 1

Apply the cosine double-angle identity.

$\cos (2 \cdot 135 °)$

Step 2

Multiply $2$ by $135 °$ .

$\cos (270)$

Step 3

Apply the reference angle by finding the angle with equivalent trig values in the first quadrant. Make the expression negative because cosine is negative in the third quadrant.

$- \cos (90)$

Step 4

The exact value of $\cos (90)$ is $0$ .

$- 0$

Step 5

Multiply $- 1$ by $0$ .

$0$