mn+m+n=2
mn+m+n+1 = 3
(m+1)(n+1) = 3
m+1=1.m= 0
n+1=3.n = 2
m+1=3.m=2
n+1=1.n = 0
m+1= -1.m= -2
n+1= -3.n = -4
m+1= -3.m= -4
n+1= -1.n = -2
m - n = ±2