. If x and y are none negative integer, x*y=?
(2) is not sufficient:
3^x = 9^y
3^x = 3^(2y)
x = 2y
All (2) tells us is that x is twice as large as y.
(1) is sufficient:
If x > 0, then 7 is a divisor of the left side of the equation. Then 7 must be a divisor of the right side. But clearly it cannot be- the only prime that can divide the right side is 13. Here, of course, we're using unique factorization into primes. So x = y = 0.
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