1/(x+y)=10
x+y=1/10
(x+y)²=1/100
x²+y²+2xy=1/100①
1/(x-y)=6
x-y=1/6
(x-y)²=1/36
x²+y²-2xy=1/36②
①+②
2(x²+y²)=17/450
x²+y²=17/900