sin12°sin87°+sin78°cos87°=______．_爱下问搜题

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问题填空题

sin12°sin87°+sin78°cos87°=______．

答案

∵12°+78°=90°，∴sin78°=cos12°

因此，sin12°sin87°+sin78°cos87°

=sin12°sin87°+cos12°cos87°=cos（12°-87°）=cos（-75°）=cos75°

∵75°=45°+30°

∴cos75°=cos45°cos30°-sin45°sin30°=

2

2

×

3

2

-

2

2

×

1

2

=

6

-

2

4

综上所述，可得sin12°sin87°+sin78°cos87°=

6

-

2

4

故答案为：

6

-

2

4

填空题

Questions 14-18

·Using the information in the text, complete each sentence 14-18 with a word or phrase from the list below.
·For each sentence (14-18), mark one letter (A-G) on the Answer Sheet.
·Do not mark any letter twice.
14. The early settlers in American ______.
15. The passage suggests that the war between French and Indians lasted ______.
16. The kind of life Indians lead in their reservation is ______.
17. The two measures that Indians had taken to improve their lives are ______.
18. From the passage, we can infer that the author ______.

A. sympathizes the American Indians
B. eighteen years
C. found the Indians very helpful
D. taking a militant stand and appealing to the courts
E. notoriously deprived
F. ask the Indians to leave their lands
G. force the Indians to leave

单项选择题 A1/A2型题

在额部，两眉头中间的腧穴是（）

A.水沟

B.攒竹

C.印堂

D.大椎

E.百会