What are exact values in trigonometry?
For certain angles, the values of sin θ, cos θ, and tan θ can be written exactly, using fractions and surds. You should be familiar with these values, and also be able to derive the values using geometry.
Exact values of sin, cos, and tan
The exact values you are expected to know are summarised in the following table:
(Note that the values of sin going from 0° to 90° match those of cos going from 90° to 0°.)