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For what value of b will the line y=-2x+b be tangent to the parabola y=3x^2+4x-1? Show work-2 marks

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2 answers
  1. you ever gonna show any of your work?

    you want the slope of the line (-2) to be the same as the slope of the parabola.

    The slope of the parabola at any point (x,y) is 6x+4

    So, if 6x+4 = -2, x = -1

    y(-1) = 6, so the line

    y = -2x+b must pass through (-1,-2)

    I think now you can find b.

    Check your work at

    http://www.wolframalpha.com/input/?i=plot+y%3D3x^2%2B4x-1%2C+y%3D-2x-4

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  2. y(-1) = -2

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