Thread: derivative of cos^3(3x)?

is it -3sin^3(3x) or did i miss something?

Originally Posted by daniels

is it -3sin^3(3x) or did i miss something?

Yes you need to use the chain rule. Twice.

let





and



Then by the chain rule you get

so then im guessing for f(x) = 2sin(2x) + e^(3x^2) + cos^3(3x)

f '(x) isn't= 4cos(2x) + 3e^(x^2) + -3sin^3(3x) ????

Originally Posted by daniels

so then im guessing for f(x) = 2sin(2x) + e^(3x^2) + cos^3(3x)

f '(x) isn't= 4cos(2x) + 3e^(x^2) + -3sin^3(3x) ????

The derivative of the first term is correct, you need to use the chain rule on the last two terms.

okay thnks