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=

1
3
,x2+y2=
5
3

故x4+y4=(x2+y22-2x2y2=

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=

1
3
,x3-y3=2代入,

可得x5-y5=

29
9

故答案为

23
9
29
9

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