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Math Help - parabola's

  1. #1
    Junior Member Dragon's Avatar
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    parabola's

    Find C so that the vertex of the parabola y=x^2-8x+c is a point on the x axis
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  2. #2
    Super Member Aryth's Avatar
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    Quote Originally Posted by Dragon View Post
    Find C so that the vertex of the parabola y=x^2-8x+c is a point on the x axis
    x value of vertex = -b/2a where b = -8 and a = 1

    8/2 = 4

    If the vertex lies on the x-axis, the y value must be zero, so we plug in the point (4, 0) to find C:

    0 = (4)^2 - 8(4) + C

    0 = 16 - 32 + C

    0 = -16 + C

    16 = C

    There you go.

    y = x^2 - 8x + 16

    To verify it even further we solve for x:

    0 = (x-4)(x-4)

    Thus x = 4
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