（x-2）平方 +|y-3|=0
∴x-2=0
y-3=0
∴x=2,y=3
原式=(x-y)/(x-y)²-y(x+y)/(x-y)(x+y)
=1/(x-y)-y/(x-y)
=(1-y)/(x-y)
=(1-3)/(2-3)
=2