Find the number of triplets of positive integers that satisfy the system of equations above.
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The second equation can be written as y ( x + z ) = 3 7 . Now as 3 7 is prime and x + z ≥ 2 we must have y = 1 , and thus x + z = 3 7 ⟹ z = 3 7 − x . The first equation now becomes
x + x z = 2 1 3 5 ⟹ x + x ( 3 7 − x ) = 2 1 3 5 ⟹ x 2 − 3 8 x + 2 1 3 5 = 0 ,
which has no real solutions, (and thus no positive integer solutions), since the discriminant 3 8 2 − 4 ∗ 2 1 3 5 < 0 . Thus there are 0 positive integer solutions ( x , y , z ) .