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Kaplan Question

This topic has 3 member replies
rajesh_ctm Master | Next Rank: 500 Posts Default Avatar
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Kaplan Question

Post Tue Apr 17, 2007 4:20 pm
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    What is the value of x^2-1?

    (1) The value of x^2 - 5x is -6


    (2) The value of (x^2 - 1)/(x + 1) is 1

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    jayhawk2001 Community Manager
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    Post Tue Apr 17, 2007 9:41 pm
    rajesh_ctm wrote:
    What is the value of x^2-1?

    (1) The value of x^2 - 5x is -6


    (2) The value of (x^2 - 1)/(x + 1) is 1
    1 - insufficient. x^2 - 5x + 6 = 0 implies x = 2 or x = 3

    2 - insufficient. (x+1)(x-1)/(x+1) = 1. We cannot cancel out
    x+1 from numerator and denominator unless we know x != -1.

    Alternatively, x^2 - 1 = x + 1. So, x^2 -x -2 = 0 implies
    x = 2 or x = -1

    Combining 1 and 2, we have x = 2.

    Is C the answer ?

    ns88 Senior | Next Rank: 100 Posts Default Avatar
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    33 messages
    Post Sun May 06, 2007 12:14 pm
    I'm getting B.

    x^2-1= (x+1) (x-1)


    (x+1) (x-1)/x+1= 1


    x-1=1

    x=2


    what's the OA?

    jayhawk2001 Community Manager
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    Post Sun May 06, 2007 1:08 pm
    ns88 wrote:
    I'm getting B.
    x^2-1= (x+1) (x-1)
    (x+1) (x-1)/x+1= 1

    x-1=1

    x=2

    what's the OA?
    ns88, you cannot cancel out x+1 from the numerator and denominator
    unless you know x != -1.

    If x=-1, then essentially you are doing 0/0 = 1 which is incorrect.

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