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Math Help - parabolas

  1. #1
    Junior Member alwaysalillost's Avatar
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    Post parabolas

    Determine (a) how many x-intercepts the parabola has and (b)whether its vertex lies above or below or on the x-axis.

    1. y = x^2 - 5x + 6

    2. y = x^2 + 2x - 1

    If you can please explain to me how to work this problem I'd be very grateful for I am greatly confused with these problems.

    PS: I'n the book it says to do it without drawing a graph of the equation so how do I find it without graphing it?
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  2. #2
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    Factorise.
    Break Brakets

    x^2 - 5x + 6

    (x - 2) (x - 3)

    Intercepts x axis at x = 2 and x = 3
    so intercepts twice.

    whether its vertex lies above or below or on the x-axis

    I would pick a number between 2 and 3 ie. 2.5 and subtitute into x^2 - 5x + 6
    If its positive answer, its above x axis.
    In this case its negative so its below.

    Try the second one.

    For the second one, x is not an integer.
    Use the quadratic formula.
    Last edited by r_maths; May 15th 2007 at 01:01 PM.
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  3. #3
    Junior Member alwaysalillost's Avatar
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    Thanks r_maths!
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