题干

阅读理解题:下面利用45°角的正切,求tan22.5°的值,方法如下:

解:构造Rt△ABC,其中∠C=90°,∠B=45°,如图.

延长CB到D,使BD=AB,连接AD,则∠D=

1
2
∠ABC=22.5°.

设AC=a,则BC=a,AB=BD= 2 a.

又∵CD=BD+CB=(1+ 2 )atan22.5°=tan∠D=

A
C
C
D
=
a
(
1
+
2
)
a
=2 ﹣1

请你仿照此法求tan15°的值.

上一题 下一题 0.0难度 选择题 更新时间:2015-01-05 06:59:37

答案(点此获取答案解析)

解:构造Rt△ABC,其中∠C=90°,∠ABC=30°,

延长CB到D,使BD=AB,连接AD,

则∠D=

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