Is \(x \geq 0?\)

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Is \(x \geq 0?\)

by M7MBA » Tue Jun 25, 2019 6:22 am

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Is \(x \geq 0?\)

\((1)\ x^2 = 9x\)
\((2) \ x = -|x| \)

The OA is the option _A_

Source: Veritas Prep
Source: — Data Sufficiency |

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by Ian Stewart » Thu Jun 27, 2019 7:31 am

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Rewriting Statement 1 with zero on one side, x^2 - 9x = 0, so x(x-9) = 0, and x = 0 or x = 9. Either way, x is greater than or equal to zero, so Statement 1 is sufficient.

Statement 2 tells us |x| = -x, which only happens when x is less than or equal to zero (when x is positive, the absolute value doesn't do anything to x, so in that case, |x| = x would be true). Since it's possible that x = 0, in which case the answer to the question is 'yes', and possible that x might be negative and the answer is 'no', Statement 2 is not sufficient, and the answer is A.
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