题目内容
如图是某重点中学学校运动场平面图,运动场总面积15000平方米,运动场是由一个矩形
和分别以
、
为直径的两个半圆组成,塑胶跑道宽8米,已知塑胶跑道每平方米造价为150元,其它部分造价每平方米80元,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408240255399823594.jpg)
(Ⅰ)设半圆的半径
(米),写出塑胶跑道面积
与
的函数关系式
;
(Ⅱ)由于受运动场两侧看台限制,
的范围为
,问当
为何值时,运动场造价最低(第2问
取3近似计算).
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824025539919534.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824025539950389.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824025539966395.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408240255399823594.jpg)
(Ⅰ)设半圆的半径
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824025540013464.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824025540028321.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824025540060260.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824025540075486.png)
(Ⅱ)由于受运动场两侧看台限制,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824025540060260.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824025540106628.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824025540060260.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824025540138309.png)
(Ⅰ)
;(Ⅱ)
.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408240255401531717.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824025540184431.png)
试题分析:(Ⅰ)塑胶跑道由两个半圆和两个矩形构成,利用圆和矩形的面积公式便可得其面积.
(Ⅱ)单位造价乘以面积便得总造价,这样可得总造价与半径的关系式:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408240255402001265.png)
试题解析:(Ⅰ)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408240255402161525.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408240255402311482.png)
(Ⅱ)总造价:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408240255402621241.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408240255402781206.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408240255402941178.png)
令
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824025540325715.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824025540340817.png)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824025540325715.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824025540106628.png)
故当
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824025540184431.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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