题目内容
如图,小明从路灯下向前走了5米,发现自己在地面上的影子长DE是2米,如果小明的身高为1.6米,那么路灯离地面的高度AB是_______米.![](http://thumb.1010pic.com/pic1/imagenew2/czsx/0/66300.png)
.(本题满分12分)
某单位在抗雪救灾中,需要在
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/0/37580.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/1/37581.gif)
6000米的
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/2/37582.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/3/37583.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/0/37580.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/1/37581.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/2/37582.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/3/37583.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/8/37588.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/9/37589.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/10/37590.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/11/37591.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/0/37580.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/1/37581.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/14/37594.gif)
位至少应该准备多长的电线?(精确到小数点后1位;参考数据:
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/15/37595.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/16/37596.gif)
5.6解:在
中,![](http://thumb.1010pic.com/pic1/imagenew2/czsx/18/37598.gif)
,
,
根据正弦定理
,……4分
在
中,![](http://thumb.1010pic.com/pic1/imagenew2/czsx/3/37603.gif)
,
,
根据正弦定理
,……8分
又在
中,
.
根据勾股定理有![](http://thumb.1010pic.com/pic1/imagenew2/czsx/9/37609.gif)
实际所需电线长度约为
(米). ………………………12分解析:
易得
略
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/17/37597.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/18/37598.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/19/37599.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/0/37600.gif)
根据正弦定理
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/1/37601.gif)
在
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/2/37602.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/3/37603.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/4/37604.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/5/37605.gif)
根据正弦定理
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/6/37606.gif)
又在
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/7/37607.gif)
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/8/37608.gif)
根据勾股定理有
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/9/37609.gif)
实际所需电线长度约为
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/10/37610.gif)
易得
![](http://thumb.1010pic.com/pic1/imagenew2/czsx/1/66301.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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