Trigonometry Examples

$\cos^{2} (120) - \sin^{2} (120)$

Step 1

Apply the cosine double-angle identity.

$\cos (2 \cdot 120)$

Step 2

Multiply $2$ by $120$ .

$\cos (240)$

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.

$- \cos (60)$

Step 4

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

$- \frac{1}{2}$

Step 5

The result can be shown in multiple forms.

Exact Form:

$- \frac{1}{2}$

Decimal Form:

$- 0.5$