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问题 填空题
已知α为锐角，且sinαcosα=
1
2
，则
1
1+sinα
+
1
1+cosα
=______．
答案

∵（sinα+cosα）2=sin2α+2cosαsinα+cos2α=1+1=2

 α为锐角

∴sinα+cosα=

2

∵

1
1+sinα
+
1
1+cosα
=
2+sinα+cosα
1+cosα+sinα+sinαcosα
=
2+
2
1+
1
2
+
2
=4-2
2

故答案为4-2

2
．

选择题

Many British people have noticed that butterflies _______ from its natural habitats during the past several years.

A．are disappearing

B．have been disappeared

C．have been disappearing

D．will have disappeared
查看答案
单项选择题

无线探测器是由探测器与（）两部分组成。

A、接收机

B、发射机

C、控制器

D、收发机
查看答案