Help I Need To Find The Derivative

[portillj72]

Help I Need To Find The Derivative!

I don't know how to find the derivative of cos(8theta)

i know there is an identity cos(2theta) but idk if I am able to expand it or not?

 

[nicksauce]

Are you familiar with the chain rule?

 

[poopcaboose]

Just make 8theta a function, then use the general power, or chain rule to differentiate. in other words you want to find dy/dtheta. So using the general power rule, or chain rule, the derivative=-sin(8theta)*(8theta')=-8sin(8theta)

 

[HallsofIvy]

nicksauce and poopcaboose are both saying that you don't need to expand it at all- just use the chain rule.