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Find the number of solutions of the equation

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Source: — Problem Solving |

by Anurag@Gurome » Mon Jun 04, 2012 10:12 pm
hey_thr67 wrote:Find the number of solutions of the equation

|x - |x - 2|| = 6
The critical point of this equation is x = 2, as for x < 2, |x - 2| = (2 - x) and for x > 2, |x - 2| = (x - 2)

Hence, we will analyze the expression at either side of x = 2.

For x < 2,
  • |x - 2| = -(x - 2) = (2 - x)
    --> |x - |x - 2|| = 6
    --> |x - (2 - x)| = 6
    --> |2x -2| = 6
    --> |x - 1| = 3
    --> x = -2 or x = 4

    But x = 4 violates our initial assumption of x < 2.
    Hence, only valid solution in this range is x = -2
For x > 2,
  • |x - 2| = (x - 2)
    --> |x - |x - 2|| = 6
    --> |x - (x - 2)| = 6
    --> |2| = 6 --> Impossible

    Hence, there are is no valid solution in this range
Therefore, total number of solutions of the given equation is 1.

The correct answer is B.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

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