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问题 填空题
已知向量
a
和
b
的夹角为60°，|
a
|=3，|
b
|=4，则（2
a
-
b
）•
a
等于______．
答案

a
•
b
=|
a
||
b
|  cos60°=3×4×
1
2
=6

（2

a
-
b
）
a
=2|
a
|2-
a
•
b
=18-6=12

故答案为：12

填空题

缺词填空。

     John (1)l_______ chocolate very much, but his mother never (2)g_______ him any. (3)B_______ she

thinks it's bad for his teeth. But John has a very kind grandfather. The old man loves him very much.

(4)S_______ he buys some chocolate for John. Then his mother will let John eat the chocolate to make the

old man happy. One evening (5)b_______ John's birthday, he is saying his prayers (祈祷) in his

(6)b_______, "Please, god," he shouts, "give me a (7)b_______ box of chocolate for my birthday."

     His mother hears his words and comes (8)i_______ the room. "Why are you shouting?" She asks,

"God can hear you when you talk quietly." "I know, but my grandfather is in the (9)n_______ room, he

can't." John (10)a_______.

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单项选择题

已知—个有序表为(12，18，24，35，47，50，62，83，90，115，134)，当二分查找值为 47的元素时，经过______次比较后查找成功。

A．1

B．2

C．3

D．4
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