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Thread: find all values of x where tangent line is horizontal

  1. #1
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    find all values of x where tangent line is horizontal

    f(x)=2x^3+9x^2-60x+4


    this polynomial is not factorable.. do I just put no x values as the answer or what should I put


    Woops.! My bad. I had to derive this whole equation with the power rule of derivative hehe
    Last edited by math951; Sep 12th 2016 at 08:47 AM.
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  2. #2
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    Re: find all values of x where tangent line is horizontal

    Well, I would use the word "differentiate" rather than "derive" but, yes, the slope of the tangent line to the graph of y= f(x), at x= a, is f'(a). A line is horizontal if and only if that slope is 0: f'(x)= 0. You need to solve f'(x)= 0.
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