Some More Trigonometric Formulas

Double- Angle Formulas:

These are used when you have a problem with a double angle (i.e. sin2x) and you want to put it in simpler terms so it is easier to solve.  

How to derive Double- Angle formulas:

 

 

Power- Reducing Formulas:
These are used when trying to get simplify a trig function that has been squared
WARNING: These are not necessarily helpful because they change the size of the angle.  They are not always a good idea to use, and they are not used often.  But we still have them because math.

 Half Angle Formulas
These are used to find angles that do not lie on the unit circle, but are half of an angle that does.

 

If you need a refresher on the sum and difference formulas, check out