Name: nagaraj
Who is asking: Other
Level: Secondary

Question:
Why 0^o , 30^o , 45^o , 60^o ,and 90^o are taken as standard angles in Trigonometry? Why can't we take some other angles as standard angles?

The angles you list are the ones that are most easily constructed using ruler and compass. Every student learns how to construct them in their first geometry class. That means that a person can solve trigonometry problems involving these angles without any need of a calculator. Other nice constructable angles are 72 degrees (which is the angle at the center of the regular pentagon), and the halves of any known angle (such as 15, 22.5, and 36).