Originally Posted by

**makarooney** I have a WebWork problem that gives me :

f(x)=[cos(2x^2)-1]/(x^3)

and it asks me to find the 9th derivative at 0. It gives me a hint that I should use the Maclaurin series of f(x).

So far, I found f(x) in summation form. I first found cos(2x^2), subtracted -1, and then divided each term by x^3. At the end I get the equation attached to this post. I don't know how to proceed...

I thought that f(9nthDerivative)(0)/9! is equal to the constants of the ninth term in the summation. i'm really stuck. Can someone help me?

Ps. sorry, I'm new to the forum and I don't know how to add equations :S