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Math Help - Derivatives Problem

  1. #1
    Newbie JBknights10's Avatar
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    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 + √2x + 1
    and f '(r) = 4
    find r.
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  2. #2
    Super Member 11rdc11's Avatar
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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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  3. #3
    Newbie JBknights10's Avatar
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    I think I messed up taking the derivative of √2x because f ' (x) came out to be like -6

    What is the derivative of √2x is it just 2?
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  4. #4
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    Quote Originally Posted by JBknights10 View Post
    I think I messed up taking the derivative of √2x because f ' (x) came out to be like -6

    What is the derivative of √2x 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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  5. #5
    Newbie JBknights10's Avatar
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    Quote Originally Posted by mr fantastic View Post
    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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  6. #6
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    Quote Originally Posted by JBknights10 View Post
    Thank you. I'm new I need to figure out how to get problems to show up so well with the math tags.
    http://www.mathhelpforum.com/math-he...-tutorial.html
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