what are the power reducing identities for trig?

Expert Answers

An illustration of the letter 'A' in a speech bubbles

Start with the identities for `cos2theta` :

(a) `cos2theta=2cos^2theta-1`


(b) `cos2theta=1-2sin^2theta`


(c) `tan^2theta=(sin^2theta)/(cos^2theta)=(1-cos2theta)/(1+cos2theta)`

(d) `sin^thetacos^2theta=((1-cos2theta)/2)((1+cos2theta)/2)`




With some algebra you can find reduction formulas for higher powers. Please see reference for these formulas.

** I find it far more useful to be able to derive the formulas than to just memorize them. You really only need to memorize a few identities, and then know how to manipulate them. Of course, in a school setting it helps to know formulas, but in the long run you will find it far more helpful to understand how to get the formulas on your own.

Approved by eNotes Editorial Team