若a的绝对值=2,b的绝对值=5且a+b的绝对值=a+b,求a-b的值

| a | = 2
a = 2 或 a = -2
| b | = 5
b = 5 或 b = -5
|a + b| = a + b
a + b ≥ 0
所以a = 2 ,b = 5 或 a = -2 ,b = 5
所以 a - b = -3 或 -7