0, 1, 2, or 3

{ x y + x z = 2135 x y + y z = 37 \large \begin{cases} xy+xz = 2135 \\ xy+yz =37 \end{cases}

Find the number of triplets of positive integers ( x , y , z ) (x,y,z) that satisfy the system of equations above.

1 2 3 0

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1 solution

The second equation can be written as y ( x + z ) = 37 y(x + z) = 37 . Now as 37 37 is prime and x + z 2 x + z \ge 2 we must have y = 1 y = 1 , and thus x + z = 37 z = 37 x x + z = 37 \Longrightarrow z = 37 - x . The first equation now becomes

x + x z = 2135 x + x ( 37 x ) = 2135 x 2 38 x + 2135 = 0 x + xz = 2135 \Longrightarrow x + x(37 - x) = 2135 \Longrightarrow x^{2} - 38x + 2135 = 0 ,

which has no real solutions, (and thus no positive integer solutions), since the discriminant 3 8 2 4 2135 < 0 38^{2} - 4*2135 \lt 0 . Thus there are 0 \boxed{0} positive integer solutions ( x , y , z ) (x,y,z) .

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