Trigonometry Examples

$\frac{2 π}{3}$

Step 1

Take the cosine of $\frac{2 π}{3}$ .

$\cos (\frac{2 π}{3})$

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 $\frac{1}{2}$ .

$- \frac{1}{2}$