在(x-2)6的展开式中，x2的系数是（） A．60 B．-402 C．30 D．-3_爱下问搜题

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问题选择题

在(x-

2

)6的展开式中，x²的系数是（　　）

A．60

B．-40

2

C．30

D．-30

2

答案

∵Tr+1=

C

r6

x6-r•(2

1

2

)r=2

r

2

•C

r6

•x6-r，

令x的指数为2，即6-r=2，r=4；

∴x²的系数为：4C₆⁴=60；可排除B、C、D．

故选A．

完形填空

     Mike had been delivering (送) newspaper for a week, but he was still not quite sure   36   he was going to like his first job. Today he was to   37   the month’s money from his customers (顾客). At the first house, Mike walked past the Pierces’ barking dog,   38   was tied up in the front yard. When he    39    the door he got up enough   40   to ring the bell. He told the man what he   41   . Mr Pierce didn’t smile or say anything , but he handed Mike a bill. Mike   42   counted out the man’s change.
43   the time he got to the   44   house, Mike felt a little more at ease. Mr Simon was repairing his   45   . He, too, gave Mike a   46   . but he smiled and talked    47    Mike gave him his   48   .
As Mike walked to the third house, he   49   a bit uneasy, Mr Swenson was just    50     home from the store, and he stopped   51   he saw Mike. Mr Swenson paid Mike the exact amount in change. They stood   52   in front of the house   53   . This wasn’t   54   to be such a difficult job    55    , thought Mike as he continued on his way.

C．for a while

填空题

车辆限界可分为3种状况，即车辆（）、车辆（）和车辆动态包络线。