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Thread: Tangent line problem

  1. #1
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    Tangent line problem

    Hello, I hope someone can help me with this problem:

    Let   f(x) = x^2 +ax+b for all x. Find values of  a and  b such that the line  y= 2x is tangent to the graph of f at the point (2,4).

    Thanks.
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  2. #2
    MHF Contributor Matt Westwood's Avatar
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    Nice one.

    First you need to find out what the gradient of the tangent is. You do that by differentiating the function. Then you look at what values for a and b give you the equation of the line you've been given.

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