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Math Help - Slope of the perpendicular line question

  1. #1
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    Slope of the perpendicular line question

    Question:

    At what point on the curve y=-2x^4 is the tangent line perpendicular to the line x-y+1=0?

    What I did was set the derivative of the curve ( -8x^3) equal to the negative slope of the second (-1 in this case) as that's how I assumed we find the perpendicular line.

    I got an answer of 2, but the book says x=1/2
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  2. #2
    Senior Member MacstersUndead's Avatar
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    -8x^3 = -1
    8x^3 = 1
    x^3 = 1/8
    x = 1/2
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