I'm completely confused by this

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- Oct 2nd 2013, 06:59 PMrhcprule3derivative of 1/x^(2/5) + 8/x^(5/7)?
I'm completely confused by this

- Oct 2nd 2013, 08:29 PMtopsquarkRe: derivative of 1/x^(2/5) + 8/x^(5/7)?
- Oct 3rd 2013, 04:55 AMrhcprule3Re: derivative of 1/x^(2/5) + 8/x^(5/7)?
yes i know, actually got what i think is the derivative and for the problem im working on, I got f'(1) correct but when I plug in 4 for f'(4) it says its incorrect! Error in the system?

What i got was -2/5(x)^(-3/5) - 5/7(8x)^(-2/7)

For f'(1) I got -6.114 and I got that correct

When I got in f' (4) I got -.4395 and it says its incorrect - Oct 3rd 2013, 06:08 AMebainesRe: derivative of 1/x^(2/5) + 8/x^(5/7)?
Another hint: f(x) can be written as:

$\displaystyle f(x) = x^{-2/5} + 8x^{-5/7}$

-2/5 -1 is not equal to -3/5. And -5/7 - 1 is not equal to -2/7.