问题 解答题
已知x2-3x+1=0,求(1)x+
1
x
;(2)x5+
1
x5
答案

(1)∵x2-3x+1=0,

∴x≠0,

方程两边同时除以x,

得x-3+

1
x
=0,

∴x+

1
x
=3;

(2)∵x+

1
x
=3,

∴(x+

1
x
2=9,(x+
1
x
3=27,

即x2+2+

1
x2
=9,x3+3x+
3
x
+
1
x3
=27,

∴x2+

1
x2
=7,x3+
1
x3
=18,

∴(x2+

1
x2
)(x3+
1
x3
)=7×18,

x5+

1
x5
+x+
1
x
=126,

x5+

1
x5
=123.

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