已知α为第二象限角，sinα=35，则sin2α=（） A．-2425 B．-12_爱下问搜题

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问题选择题

已知α为第二象限角，sinα=

3

5

，则sin2α=（　　）

A．-

24

25

B．-

12

25

C．

12

25

D．

24

25

答案

因为α为第二象限角，sinα=

3

5

，

所以cosα=-

1-sin2α

=-

4

5

．

所以sin2α=2sinαcosα=-2×

3

5

×

4

5

=-

24

25

．

故选A．

完形填空

Tom is a middle school student. He is studying in Grade 7. He usually     at 7:00 o’clock in the morning.       today he gets up at 6:30 and goes to buy a big       . After that he helps his grandparents clean their room, because it is his         birthday. His grandpa is going to be 68 years old.
Tom      two CDs about Beijing Opera(京剧)      his grandpa. He is sure his grandpa would like      very much, because his grandpa        listening to Beijing Opera.
When Tom        home at noon, his mother is making        with grandma. They are laughing and talking about something         . His grandpa is drinking tea         listening to Beijing Opera.
Tom says, “Happy birthday to you, grandpa.” Then he        the big cake and gives grandpa a         piece. Grandpa is very happy and eats it.
In the evening, Tom watches TV with his grandparents together. He is a little        but very happy, because he can make his grandparents happy.

A．goes to school

D．goes to bed

C．grandpa’s

D．grandma’s

单项选择题

用万用表测量晶体管参数时，应用（）挡。

A.R×1

B.R×10

C.R×1k

D.R×10k