If the function y = (2 + m) XM2 − 3 is a positive proportional function, then the value of the constant M is______ .

If the function y = (2 + m) XM2 − 3 is a positive proportional function, then the value of the constant M is______ .

From the definition of positive proportion function, we can get: m2-3 = 1, and M + 2 ≠ 0, the solution is: M = ± 2. ∧ M = 2, so the answer is 2