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Math Help - tangent line/normal line

  1. #1
    Newbie
    Joined
    Sep 2008
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    Question tangent line/normal line

    Find the equation of the tangent line and the normal line for

    y=(1+2x)^2 on point (1,9)

    I tried to find the slope by finding f' but i don't think I am doing it right.
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  2. #2
    Super Member
    Joined
    Jun 2008
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    792
    The derivative is the slope of the tangent line. The derivative of y = (1+2x)^2 is:
    \frac{dy}{dx} = 4(1+2x)

    Given the point (1, 9) and a slope, you can find the equation of the line by
    y - y_1 = m(x-x_1)

    The equation of the normal line passes thru point (1, 9) but has a slope given by:

    m_{normal} \cdot m_{tangent} = -1
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