(x-12x2)9的展开式中常数项是______.(用数字作答)-数学

题目简介

(x-12x2)9的展开式中常数项是______.(用数字作答)-数学

题目详情

(x-
1
2x2
)9
的展开式中常数项是______.(用数字作答)
题型:填空题难度:中档来源:不详

答案

(x-class="stub"1
2x2
)9
的通项是
Cr9
x9-r(-class="stub"1
2x2
)
r
=
Cr9
(-class="stub"1
2
)
r
x9-3r

∵要求展开式中常数项,
∴9-3r=0,
∴r=3,
C39
(-class="stub"1
2
)
3
=-class="stub"84
8
=-10.5,
故答案为:-10.5.

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