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Math Help - equation of the line tangent...

  1. #1
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    equation of the line tangent...

    given f(x)=7-15x+(9x^2)-(x^3)
    Write an equation of the line tangent to the graph of f at x=2.

    i know i have to find the derivative and plug in 2 for x, giving me 9 as the slope, but since they dont give us a point, is the equation just
    y-y1=9(x-x1) ?? or would it be y=9x??

    please help. thanks!!
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  2. #2
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    They do give you a point, they tell you they want the line tangent at x=2. To find the coordinate of where they want the line tangent, plug x=2 into the original function to get the y-coordinate.
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