已知如果x+y=1,x2+y2=2,那么x4+y4=
问题描述：
已知如果x+y=1,x2+y2=2,那么x4+y4=
答
(x+y)²=x²+2xy+y²
2xy=(x+y)²-(x²+y²)=1-2=-1
xy=-1/2
x4+y4
=(x²+y²)²-2(xy)²
=2²-2×¼
=3.5