问题
填空题
若x-y=1,x3-y3=2,则x4+y4=______,x5-y5______.
答案
∵x3-y3=(x-y)(x2+xy+y2)=2,
x-y=1,
x3-y3=(x-y)(x2+xy+y2)=2,
又∵x2-2xy+y2=1,与上式联立得:
xy=
,x2+y2=1 3
,5 3
故x4+y4=(x2+y2)2-2x2y2=
,23 9
又x5-y5=x5-x4y+x4y-xy4+xy4-y5=x4(x-y)+xy(x3-y3)+y4(x-y),
将x-y=1,xy=
,x3-y3=2代入,1 3
可得x5-y5=
,29 9
故答案为
、23 9
.29 9