问题 填空题
若(2
x
-
1
x
n的展开式中所有二项式系数之和为64,则展开式的常数项为______.
答案

因为(2

x
-
1
x
n的展开式的二项式系数之和为64,所以2n=64,所以n=6,
由二项式定理的通项公式可知 Tr+1=
Crn
(2
x
6-r(-
1
x
r=26-r(-1)r C
 r6
x3-r
当r=3时,展开式的常数项为:23(-1)3C
 36
=-160.
故答案为:-160.

选择题
材料分析题

目前我国的注册志愿者总人数已达2511万;从1993年到目前为止,全国累计已有2.68亿人次的志愿者为全社会提供了61亿小时的志愿服务。

(1)请结合所学知识,简要分析为什么有越来越来多的人到志愿者服务的行列中来?

                                                                                                                                                              

(2)参加志愿服务活动,志愿者们会付出怎样的代价?又会获得怎样的回报?

                                                                                                                                                               

                                                                                                                                                               

                                                                                                                                                               

(3)你认为作为一名合格的志愿者,最重要的是具备什么精神?

                                                                                                                                                               

(4)热心公益、服务社会,是志愿者们共有的品质和自觉行动。你参加过哪些社会公益活动?有什么体会?