Question

What is the derivative of x^3(x-4) ?

Answer 1

you are better off foiling it then taking derivative

Answer 2

agreed^

Answer 3

I did try the product rule and I got 3x^2(x-4) + x^3 , but I wasn't sure if it was correct

Answer 4

If I foil it, I get 4x^3 -12x^2 . That doesn't seem right, does it?

Answer 5

yup x^4 - 4x^3
differentiating gives

4x^3 - 12x^2

Answer 6

Noitce what you got for the product rule: 3x^2(x-4) + x^3

now distriute that 3x^2 into the parenthese:

3x^3-12x^2+x^3, gather like terms and you geT: 4x^3-12x^2

Answer 7

Thus we see that wheter you chooe to foild first, or apply the product rule, you will get the same answer

Answer 8

Oh ok! Thanks!