Find the number of ordered pairs of positive integers such that the following equation is satisfied,
where .
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Let x = z x ′ and y = z y ′ . Then the equation turns into z 3 x ′ 3 + z 2 y ′ 2 + z = z 3 x ′ y ′ or z 2 x ′ 3 + z y ′ 2 + 1 = z 2 x ′ y ′ Since the RHS is divisible by z it follows that the LHS is also divisible by z , so z ∣ 1 ⟹ z = 1 and our original equation reduces to x 3 + y 2 + 1 = x y ⟹ y 2 − x y + ( x 3 + 1 ) = 0
Since y is a real number, the discriminant of the quadratic w.r.t y must be positive, i.e x 2 − 4 ( x 3 + 1 ) ≥ 0 ⟹ x 2 ≥ 4 x 3 + 4 which clearly cannot be satisfied if x is a positive integer; thus, there are no solutions.