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Math Help - tangent line prob

  1. #1
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    tangent line prob

    At what point on the graph of y= 1/2x^2 is the tangent line parallel to the line 2x-4x=3?

    I took the derivative of the first equation, and set it equal to the slope of the second and got that x was equal to 1/2. Then I plugged that back into the first equation to get that the y coordinate would be 1/8. However, the answer states that the y coordinate is -1/2. the only way to get that is to plug x=1/2 into the second equation. why do you use the second equation to find the point on the graph of the first? Thanks!
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  2. #2
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    Quote Originally Posted by abcocoa View Post
    At what point on the graph of y= 1/2x^2 is the tangent line parallel to the line 2x-4x=3?

    I took the derivative of the first equation, and set it equal to the slope of the second and got that x was equal to 1/2. Then I plugged that back into the first equation to get that the y coordinate would be 1/8. However, the answer states that the y coordinate is -1/2. the only way to get that is to plug x=1/2 into the second equation. why do you use the second equation to find the point on the graph of the first? Thanks!
    Hello,

    first: There must be a typo in the equation of the line. I assume that you mean: 2x - 4y = 3.
    Your results are correct so far.

    Maybe you misread the problem? Howexactly is the text of the problem?

    EB
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  3. #3
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    nevermind

    the answer in the back of the book was incorrect, so now i know how to do the prob. Thanks anyway.
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