Skip to content

Learn Precalculus The unit circle

Exact trig values

Use the reference angle, then the quadrant for the sign.

Precalculus: The unit circle

Find the reference angle.
Remember its value.
Choose the sign from the quadrant.

Work through it

$sin \frac{2 π}{3}$

The reference angle is $\frac{π}{3}$ .

Sine is positive in Quadrant II.

$\frac{3}{2}$

$cos π$

The point is $(- 1, 0)$ .

$cos π = - 1$

Watch out for this

$cos \frac{5 π}{6} = \frac{3}{2}$

Cosine is negative in Quadrant II, so it's $- \frac{3}{2}$ .

Your turn

PreviousRadians NextUnit check

Want help with this?

Book a free consultation, and we'll help you make a plan.

Book a free consultation