(1)已知x+y=6,x²-y²=5,
x^2-y^2
=(x+y)(x-y)=5
x-y=5/(x+y)
=5/6
（2）若x+y=3,x²+y²=5
(x+y)^2=3^2=9
x^2+2xy+y^2=9
2xy=9-(x^2+y^2)
=9-5=4
xy=2