What is the value of x*?

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apoorva.srivastva
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Topic: What is the value of x*?

Sat Nov 21, 2009 12:58 am

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For all integers n, n*=n (n-1). What is the value of x*?

(1.) X*=X
(2.) (X - 1 ) * = (X - 2)

OA after some discussion !! :)

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Sat Nov 21, 2009 9:13 am

I choose B

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Thu Dec 03, 2009 8:29 pm

D because from 1 we get x^2 = 0, therefore x has to be 0.

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Thu Dec 03, 2009 9:49 pm

apoorva.srivastva wrote: For all integers n, n=n (n-1). What is the value of x? (1.) X=X (2.) (X - 1 ) = (X - 2) OA after some discussion !! Let's actually look at the algebra. (1) x* = x We also know that x* = x(x-1), so: x(x-1) = x x^2 - x = x subtracting x from both sides: x^2 - 2x = 0 x(x-2) = 0 x = 0 OR x = 2... insufficient. (2) (x-1)* = (x-2) We also know that (x-1)* = (x-1)(x-1-1) = (x-1)(x-2) = x^2 - 3x + 2, so: x^2 - 3x + 2 = x - 2 subtracting x from both sides and adding 2 to both sides: x^2 - 4x + 4 = 0 (x-2)(x-2) = 0 We have a perfect square, therefore x = 2... sufficient. Choose B. _________________ Stuart Kovinsky, B.A. LL.B. Academic Manager Admissions Consultant Kaplan Test Prep & Admissions Toronto Office 1-800-KAP-TEST GMAT Blogs Learn more about me