Find the Exact Value cos(2/3pi)

$\cos (\frac{2}{3} π)$

Step 1

Combine $\frac{2}{3}$ and $π$ .

$\cos (\frac{2 π}{3})$

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.

$- \cos (\frac{π}{3})$

Step 3

The exact value of $\cos (\frac{π}{3})$ is $\frac{1}{2}$ .

$- \frac{1}{2}$

Step 4

The result can be shown in multiple forms.

Exact Form:

$- \frac{1}{2}$

Decimal Form:

$- 0.5$

Find the Exact Value cos(2/3pi)

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