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Choosing and rejecting inequality

  1. Jan 25, 2009 #1
    1. The problem statement, all variables and given/known data
    y = |(x-2)(x-4)| and y = 6 -2x

    find the exact values for which these two equation equal each other


    2. Relevant equations



    3. The attempt at a solution

    Right I got it down to

    [tex]2 \pm \sqrt{2}[/tex] and [tex]4 \pm \sqrt{2}[/tex] and

    and i've sketched the graph, however how do i work out which values to reject and which to use?

    Thanks :)
     
  2. jcsd
  3. Jan 25, 2009 #2

    Mark44

    Staff: Mentor

    You should have two cases: one for 2 < x < 4 and the other for x < 2 or x > 4. These two cases correspond to the intervals where (x - 2)(x - 4) is negative and positive, respectively.

    For the case 2 < x < 4, I solved the quadratic equation x^2 - 8x + 14 = 0. My solutions were 4 +/- sqrt(2). Since 4 + sqrt is larger than 4, it doesn't meet the restriction that 2 < x < 4, so I would discard it.

    Is that enough help?
     
  4. Jan 26, 2009 #3
    yes, thankyou I think I see what your saying

    I will do some pratice questions

    Thanks :)
     
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