（2X+3）^2 + |-y+2| = 0
因为两项都是非负数,但是和为0,所以二者都是0
所以x = -3/2,y = 2
X的Y次方减XY
= (-3/2)^2 - 2*(-3/2)
= 9/4 + 3
= 21/4