Precalculus Examples

$\cos (960)$

Step 1

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

$\cos (240)$

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 third quadrant.

$- \cos (60)$

Step 3

The exact value of $\cos (60)$ is $\frac{1}{2}$ .

$- \frac{1}{2}$

Step 4

The result can be shown in multiple forms.

Exact Form:

$- \frac{1}{2}$

Decimal Form:

$- 0.5$