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Math Help - Solving for x in derivative = 0

  1. #1
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    Unhappy Solving for x in derivative = 0

    Thank you in advance for your help.

    I have found the derivative of f(x) from a previous problem, and now I must set the derivative to 0 since I am now finding the function of x values where the tangent is horizontal, meaning that the slope is 0.

    Here is where I am in the problem:

    3x^2-8x-7=0

    in an attempt to move x to one side and numbers to the other:

    x^2-8x=7(1/3)

    since x^2=2x

    2x-8x=7(1/3)

    But how do I get rid of the two x's since there is only supposed to be one x on the left side?

    Sorry, I'm stuck!
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  2. #2
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    Quote Originally Posted by theredqueentheory View Post
    Thank you in advance for your help.

    I have found the derivative of f(x) from a previous problem, and now I must set the derivative to 0 since I am now finding the function of x values where the tangent is horizontal, meaning that the slope is 0.

    Here is where I am in the problem:

    3x^2-8x-7=0

    in an attempt to move x to one side and numbers to the other:

    x^2-8x=7(1/3)

    since x^2=2x

    2x-8x=7(1/3)

    But how do I get rid of the two x's since there is only supposed to be one x on the left side?

    Sorry, I'm stuck!
    3x^2-8x-7=0

    Use the quadratic formula: x = \frac{-b \pm \sqrt{b^2-4ac}}{2a}

    If, x^2 = 2x (which is unusual) then 2x-8x = \frac{7}{3} is equal to -6x = \frac{7}{3}
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