题目内容
(2012•宁夏)如图,一根5m长的绳子,一端拴在互相垂直的围墙墙角的柱子上,另一端拴着一只小羊A(羊只能在草地上活动),那么小羊A在草地上的最大活动区域面积是( )![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131019110408825378488/SYS201310191104088253784006_ST/images0.png)
A.
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131019110408825378488/SYS201310191104088253784006_ST/0.png)
B.
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131019110408825378488/SYS201310191104088253784006_ST/1.png)
C.
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131019110408825378488/SYS201310191104088253784006_ST/2.png)
D.
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131019110408825378488/SYS201310191104088253784006_ST/3.png)
【答案】分析:小羊A在草地上的最大活动区域是一个扇形+一个小扇形的面积.
解答:
解:大扇形的圆心角是90度,半径是5,
所以面积=
=
m2;
小扇形的圆心角是180°-120°=60°,半径是1m,
则面积=
=
m2,
∴小羊A在草地上的最大活动区域面积=
+
=
m2,
故选D.
点评:本题的关键是从图中找到小羊的活动区域是由哪几个图形组成的,然后分别计算即可.
解答:
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131019110408825378488/SYS201310191104088253784006_DA/images0.png)
所以面积=
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131019110408825378488/SYS201310191104088253784006_DA/0.png)
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131019110408825378488/SYS201310191104088253784006_DA/1.png)
小扇形的圆心角是180°-120°=60°,半径是1m,
则面积=
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131019110408825378488/SYS201310191104088253784006_DA/2.png)
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131019110408825378488/SYS201310191104088253784006_DA/3.png)
∴小羊A在草地上的最大活动区域面积=
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131019110408825378488/SYS201310191104088253784006_DA/4.png)
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131019110408825378488/SYS201310191104088253784006_DA/5.png)
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131019110408825378488/SYS201310191104088253784006_DA/6.png)
故选D.
点评:本题的关键是从图中找到小羊的活动区域是由哪几个图形组成的,然后分别计算即可.
![](http://thumb2018.1010pic.com/images/loading.gif)
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