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SOLUTION
If x is an integer, is \(9^x + 9^{-x} = b\) ?
(1)\(3^x + 3^{-x} = \sqrt{b + 2}\) --> square both sides -->\(9^x+2*3^x*\frac{1}{3^x}+9^{-x}=b+2\) -->\(9^x + 9^{-x} = b\) . So answer to the question is YES. Sufficient.
(2) x > 0. No sufficient.
Answer: A.
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