若数列{an}的通项an=Cn6(-12)n,Sn为数列{an}的前n项和,则S6=______.-数学

题目简介

若数列{an}的通项an=Cn6(-12)n,Sn为数列{an}的前n项和,则S6=______.-数学

题目详情

若数列{an}的通项an=
Cn6
(-
1
2
)
n
,Sn为数列{an}的前n项和,则S6=______.
题型:填空题难度:中档来源:上海模拟

答案

an=
Cn6
(-class="stub"1
2
)
n

∴S6=
C16
(-class="stub"1
2
)
1
+
C26
(-class="stub"1
2
)
2
+
C36
(-class="stub"1
2
)
3
+
C46
(-class="stub"1
2
)
4
+
C56
(-class="stub"1
2
)
5
+
C66
(-class="stub"1
2
)
6

=(1-class="stub"1
2
)6-1
=-class="stub"63
64

故答案为:-class="stub"63
64

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