Are you really saying that you do not know ?
To find the value of the trigonometric functions of the angles 30, 45, and 60, we use the special 45-45-90 and 30-60-90 triangles:
Special right triangles - Wikipedia, the free encyclopedia
You can also find values of an angle whose sum/difference is two of the mentioned angles using the sum/difference identities.
Magentarita: yes, you are right.