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Tangent line of a line

  1. May 1, 2010 #1
    We know that the slope of the tangent line at a point on a curve is found by evaluating the derivative of the curve at that point.

    Say we have the curve y=2x.
    Say I wanted to find the tangent line at x=4
    The first derivative is a constant, which is not surprising since the curve is always changing at the same rate.
    However, since the first derivative is a constant, how can I find the equation of the tangent line at x=4? We can't say it's y=2 since that line does not intersect y=2x at x=4.

    Can anyone help me
  2. jcsd
  3. May 1, 2010 #2


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    The tangent to a line is the line itself.
  4. May 1, 2010 #3
    Ohhh I forgot you needed to multipliy the slope by x. Thank you very much
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