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问题 填空题
在△ABC中，若cosA=-
5
13
，则sin
A
2
=______．
答案

在△ABC中，∵cosA=-

5
13
，∴A为钝角，∴sin
A
2
＞0．

由二倍角公式可得 cosA=-

5
13
=1-2sin2
A
2
，解得sin
A
2
=
3
13
13
，

故答案为：

3
13
13
．

句型转换

按要求变换句型。

1. He used to walk to school.(改为一般疑问句)

    _____ he ____ to walk to school.

2. Danny asked  Sandy  if she could swim.(改为直接引语)

    Danny asked, “_____ _____ swim,Sandy?”

3. Simon said, “I am very busy.”(改为间接引语)

    Simon said that_____ _____ very busy.

4. The teacher said to him, “Don’t sleep in class.”(改为间接引语)

    The teacher told him_____ _____ ____ in class.

5. His uncle is a doctor.(对划线部分提问)

    _______ _____ his uncle_______?

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单项选择题

光滑铜管的直径为75mm，沿程阻力系数λ=0.021，当通过流量Q=0.005m3/s时，管壁切应力τ0为( )。

A．(A) 3.36Pa

B．(B) 1.26Pa

C．(C) 2.39Pa

D．(D) 0.95Pa
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