（x + a)(x + b) = x^2 + ( a + b)x + ab
因为：（x + a)( x + b) = x^2 + mx + 12
所以,x^2 + (a + b)x + ab = x^2 + mx + 12
因此 ab = 12,m = a + b
因为a,b,m都是整数
所以,由ab = 12得,a,b的可能取值有：
a =1,b=12; a=-1,b= -12; a=3,b=4; a = -3,b = -4; a = 2,b = 6;a = -2,b = -6
或 a =12,b=1; a = -12,b=-1; a=4,b=3; a = -4,b = -3; a = 6,b = 2; a =-6,b = -2
由上述讨论可知：
m = a+b 的可能取值有
当a =1,b=12或a =12,b=1时,m = 13
当a=-1,b= -12或a = -12,b=-1时,m = －13
当a=3,b=4或a=4,b=3时,m = 7
当 a = -3,b = -4或a = -4,b = -3时,m = －7
当 a = 2,b = 6 或a = 6,b = 2时,m = 8
当a = －2,b = －6 或a = －6,b = －2时,m = －8
（注：因为ab = 12,所以a、b不可能一正一负）