Hey helpful member of this forum, I am currently in a calculus and vectors self learning course, and I need help with a problem. ***As I wrote this thread I was doing all the math again. I found that my problem is my finding of the derivative of . I kept the rest of my solution up just incase this is also a problem. My main concern, however, is my bold statement showing where the main problem (I think) is.***

Question:Use the chain rule to find dy/dx at the indicated value of x.

My solution:

Basically how the text explains the chain rule is: "If f and g are functions having derivatives, then the composite function has a derivative given by "

So with this information this is how my solution looks:

First I expanded :

Which makes it easier for me to find the derivative (just me likely):

I believe this is where the problem lies!!! So help in finding the derivative here would be awesome!!!

Then I found the derivative of :

*

*According to wolfram alpha, this derivative is incorrect. I do not understand why. The solution on wolfram alpha when I input is . I do not understand how they come to this answer.* Link: http://www.wolframalpha.com/input/?i=y+%3D+u%28u^2+%2B+3%29^3

Assuming the above is correct, subbing into should *assuming the answer in the book is correct* come to 320 when I sub in -2 for x. So:

Then I sub in x = -2:

Then multiply by 2x + 6:

When I use the derivative shown on wolfram alpha I do get 320. *I tried this before but did not get correct answer, just tried again now and did!!!* How do I find the derivative shown on wolfram alpha?

Sub in x = -2:

*multiply by (2x + 6) with x = -2 subbed in*

- Thanks for looking at my thread!