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by **Cafe au lait** on Tue Jan 04, 2011 3:38 am

I got f'(x)=[(x^2-4)^2(20)-2(x^2-4)(2x)(20x)]/(x^2-4)^4
=(-80x^4+340x^2-80)/(x^2-4)^3
and simplify

But I am pretty sure my first step was wrong, like I did the chain or product rule wrong because my answer does not match up to what my TI-89 says it is supposed to be.

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by **Martingale** on Tue Jan 04, 2011 4:09 am

Cafe au lait wrote:I got f'(x)=[(x^2-4)^2(20)-2(x^2-4)(2x)(20x)]/(x^2-4)^4
=(-80x^4+340x^2-80)/(x^2-4)^3
and simplify

But I am pretty sure my first step was wrong, like I did the chain or product rule wrong because my answer does not match up to what my TI-89 says it is supposed to be.

$\frac{(x^2-4)^2(20)-2(x^2-4)(2x)(20x)}{(x^2-4)^4}$

$\Rightarrow\frac{20(x^2-4)\left[(x^2-4)-2(2x)(x)\right]}{(x^2-4)^4}$

$\Rightarrow\frac{20\left[x^2-4-4x^2\right]}{(x^2-4)^3}$

$\Rightarrow\frac{20\left[-3x^2-4\right]}{(x^2-4)^3}$

$\Rightarrow\frac{-20\left[3x^2+4\right]}{(x^2-4)^3}$

by **Cafe au lait** on Tue Jan 04, 2011 5:48 am

That's the answer my calculator gave me! Very helpful, thank you.

by **Martingale** on Tue Jan 04, 2011 5:52 am

Cafe au lait wrote:... to what my TI-89 says it is supposed to be.

Cafe au lait wrote:That's the answer my calculator gave me! ...

I know. You are not the only one with a ti-89 :wink:

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First step to finding the derivative of 20x/(x^2-4)^2

First step to finding the derivative of 20x/(x^2-4)^2

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Re: First step to finding the derivative of 20x/(x^2-4)^2

Re: First step to finding the derivative of 20x/(x^2-4)^2