|x|=3 x=3或-3 |y|=5 y=5或-5 |x-y|=|x|+|y| |x|=3 |y|=5 |x|+|y|=8 |x-y|=8
x-y=8或-8 由此可得 y=5 x=-3 或y=-5 x=3 x+y=2或-2 x-y=8或-8