x-y=9,xy=8.x^2+y^2=?
问题描述:
x-y=9,xy=8.x^2+y^2=?
答
x-y=9
===>(x-y)^2=81
===>x^2-2xy+y^2=81
xy=8
===>2xy=16
===>x^2+y^2=81+2xy=81+16=97