Trigonometry Examples

$\cos (180 - 60)$

Step 1

Subtract

$60$ from

$180$ .

$\cos (120)$

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.

$- \cos (60)$

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:

$- 0.5$