Any idea? Please help.

Problem Solving — algebra and arithmetic (GMAT Focus Edition)
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Source: — Quantitative Reasoning |

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by shankar.ashwin » Wed Nov 02, 2011 10:24 pm
(1) is obviously sufficient. Substitute any odd number for 'x' and it works.

Now you know the expression would hold true for all odd values of 'x'.

(2) says "Each prime factor of x^2 is >7. 2 is the only even prime and 2^2 = 4.
Now this is not possible because given x^2>7. All other prime numbers are odd. So 'x' is odd again. D