(1)已知x+y=6,x²-y²=5,求x-y的值（2）若x+y=3,x²+y²=5,求xy的值

(1)已知x+y=6,x²-y²=5,求x-y的值（2）若x+y=3,x²+y²=5,求xy的值
(1)已知x+y=6,x²-y²=5,求x-y的值（2）若x+y=3,x²+y²=5,求xy的值

(1)已知x+y=6,x²-y²=5,求x-y的值（2）若x+y=3,x²+y²=5,求xy的值
(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

x²-y²=（x-y）（x+y）=5，∴x-y=5/6
(x+y)²=x²+y²+2xy=5+2xy=3²=9
∴xy=2

x²-y²=(x+y)×(x-y)=6×(x-y)=5 则x-y=5/6
(x+y)²=x²+y²+2xy
带入为3²=5+2xy
则xy=2