(1)已知:x+1x=2,试求出x2+1x2的值;(2)已知:x2-2x-1=0,你能求出x2x4+1的值吗?-数学

题目简介

(1)已知:x+1x=2,试求出x2+1x2的值;(2)已知:x2-2x-1=0,你能求出x2x4+1的值吗?-数学

题目详情

(1)已知:x+
1
x
=2,试求出x2+
1
x2
的值;
(2)已知:x2-2x-1=0,你能求出
x2
x4+1
的值吗?
题型:解答题难度:中档来源:不详

答案

(1)x2+class="stub"1
x2
=(x+class="stub"1
x
)2-2,
∵x+class="stub"1
x
=2,
∴x2+class="stub"1
x2
=(x+class="stub"1
x
)2-2=4-2=2;
(2)能求出.
∵x2-2x-1=0,
∴x2-1=2x,
x2
x4+1 
=
x2
(x2-1) 2+2x2
=
x2
4x2+2x2
=class="stub"1
6

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