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$Old$ October 8th, 2008, 03:47 PM

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$Default$ Derivatives Problem

I have the calculator portion of my Ch. 3 Calculus test tomorrow, titled Derivatives.

I'm doing a review sheet right now, and am stuck on a problem.

If f(x) = 13 - 8x + √2x² + 1
and f '(r) = 4
find r.

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$Old$ October 8th, 2008, 04:42 PM

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Just take the derivative of your 1st function and set it equal to 4 and replace x with r. Solve for r.

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$Old$ October 8th, 2008, 05:20 PM

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I think I messed up taking the derivative of √2x² because f ' (x) came out to be like -6

What is the derivative of √2x² is it just 2?

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$Old$ October 8th, 2008, 05:42 PM

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I think I messed up taking the derivative of √2x² because f ' (x) came out to be like -6

What is the derivative of √2x² is it just 2?

No, the derivative of $\sqrt{2} \, x^2$ with respect to x is $2 \sqrt{2} \, x$ .

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$Old$ October 8th, 2008, 06:01 PM

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No, the derivative of $\sqrt{2} \, x^2$ with respect to x is $2 \sqrt{2} \, x$ .

Thank you. I'm new I need to figure out how to get problems to show up so well with the math tags.

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$Old$ October 8th, 2008, 09:29 PM

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Thank you. I'm new I need to figure out how to get problems to show up so well with the math tags.

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