Precalculus Examples

$\cos (- 540)$

Step 1

Add full rotations of $360$ ° until the angle is between $0$ ° and $360$ °.

$\cos (180)$

Step 2

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 second quadrant.

$- \cos (0)$

Step 3

The exact value of $\cos (0)$ is $1$ .

$- 1 \cdot 1$

Step 4

Multiply $- 1$ by $1$ .

$- 1$