Find the Exact Value cos(-420 degrees )

$\cos (- 420 °)$

Step 1

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

$\cos (300)$

Step 2

Apply the reference angle by finding the angle with equivalent trig values in the first 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:

$0.5$