x²+y²-6x+4y+13=0
x²-6x+9+y²+4y+4=0
(x-3)²+(y+2)²=0
∴x-3=0
y+2=0
∴x=3
y=-2
∴x的y次方=3的(-2)次方=1/9
4x²-4xy+y²+y²+6y+9=0
(2x-y)²+(y+3)²=0
2x-y=0
y+3=0
∴x=-3/2
y=-3
xy=-3/2×(-3)=9/2