Trigonometry Series (Part 3)

The following identities come in very useful when we are solving equations of trigonometric functions.

This is the basic identity

and these two can be derived from the first identity


taking note that



These following angle-identities can easily be derived if we take a look at the graphs of he respectively functions (see Trigonometry Series (Part 1)).






Consider any triangle, it need not be right-angled,



then there are two laws that can help us to calculate angles or side length of a triangle, given that we have the information about three other angles and/or sides of the triangle.
 
Law of Sines

 

Law of Cosines:



Next time we take a look at some useful formulas.