（x-2)的2次方+|y+3|=0 平方数和绝对值大于等于零,则有: x-2=0 y+3=0 x=2,y=-3 x+y=-1
(x-2)+|y+3|=0 ==> x -2 = 0 y +3 =0 ==> x =2, y = -3 x +y = 2 + (-3) = -1
