f(x)=x^3-5x^2+x , f(x+h)-f(x)/h, h cannot = 0

so far i got this

3x^2h+3xh^2+h^3-10xh-5h^2+h/H

i just need the correct answer so to see what i did or did not do.

Printable View

- Nov 9th 2009, 09:16 PMflexusFind the difference quotient and simplify answer
f(x)=x^3-5x^2+x , f(x+h)-f(x)/h, h cannot = 0

so far i got this

3x^2h+3xh^2+h^3-10xh-5h^2+h/H

i just need the correct answer so to see what i did or did not do. - Nov 9th 2009, 09:28 PMDebsta
Now factorise h out of the top to get h(....) and then cancel the h's.

- Nov 9th 2009, 09:35 PMflexus
ok now if i factor out h then i get

h(3x^2+3xh+h^2-10x-5h)/h

which = 3x^2+3xh+h^2-10x-5h

for some reason this doesnt look right to me what did i do wrong???? - Nov 9th 2009, 09:40 PMDebsta
you've lost a "+1" at the end

- Nov 9th 2009, 09:48 PMflexus
your not helping what is the answer?? im so stuck? i know i lost the +1 at the end. whats next?

- Nov 9th 2009, 09:50 PMDebsta
I actually think I am helping - I'm just not doing it for you ....there's a difference!

What is the actual question...because you have "found the difference quotient and simplified the answer". Are you supposed to now go on and take the limit as h approaches 0? - Nov 9th 2009, 09:53 PMflexus
- Nov 9th 2009, 09:57 PMDebsta
Apology accepted :). Don't put yourself down. What you have done so far is right (except for losing the +1 at the end, which is easy to do). Can you please quote the qusetion word for word?

- Nov 9th 2009, 10:06 PMflexus
- Nov 9th 2009, 10:08 PMDebsta
Can you show me the answer in the book - so I can see if it is just in a different form?

- Nov 9th 2009, 10:11 PMflexus
- Nov 9th 2009, 10:14 PMDebsta
Glad to help!