a的绝对值是2分之1,b的绝对值是3分之一,求a-b等于几

|a| = 1/2,a = 1/2,a = -1/2
|b| = 1/3,b = 1/3,a = -1/3
1.a = 1/2,b = 1/3,a - b = 1/2 - 1/3 = 1/6
2.a = -1/2,b = 1/3,a -b = -1/2 - 1/3 = -5/6
3.a = 1/2,b = -1/3,a - b = 1/2 + 1/3 = 5/6
4.a = -1/2,b = -1/3,a - b = -1/2 + 1/3 = -1/6