limn→∞a[1+4+7+…+(3n-2)]7n2-5n-2=6,则a=______.-数学

题目简介

limn→∞a[1+4+7+…+(3n-2)]7n2-5n-2=6,则a=______.-数学

题目详情

lim
n→∞
a[1+4+7+…+(3n-2)]
7n2-5n-2
=6
,则a=______.
题型:填空题难度:中档来源:长宁区一模

答案

lim
n→∞
a[1+4+7+…+(3n-2)]
7n2-5n-2
=6

lim
n→∞
a[class="stub"n
2
(1+3n-2)]
7n2-5n-2
=6,
lim
n→∞
class="stub"3a
2
n2-class="stub"a
2
n
7n2-5n-2
=6,
class="stub"3a
2
7
=6

解得a=28.
故答案为:28.

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