Trigonometry Examples

$\cos (- 180 °)$

Step 1

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 2

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

$- 1 \cdot 1$

Step 3

Multiply $- 1$ by $1$ .

$- 1$