若x+1x=3,则x4+x2+1x2=()A.5B.6C.7D.8-数学

题目简介

若x+1x=3,则x4+x2+1x2=()A.5B.6C.7D.8-数学

题目详情

x+
1
x
=3
,则
x4+x2+1
x2
=(  )
A.5B.6C.7D.8
题型:单选题难度:偏易来源:不详

答案

∵若x+class="stub"1
x
=3

∴两边平方得:x2+class="stub"1
x2
+2=9,
∴x2+class="stub"1
x2
=7
∴原式=(x4+x2+1)×class="stub"1
x2
=x2+class="stub"1
x2
+1=7+1=8.
故选D.

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