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第二十八章　圆
28.1 圆的概念及性质
INCLUDEPICTURE"复习回顾.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\复习回顾.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\复习回顾.tif" \* MERGEFORMATINET
1．在同一个圆里，所有的半径都________，所有的直径都________，且________是________的2倍．
2．有一个圆形花池的半径是10米，如果绕其周围走一圈，至少需要走________米．(π取3.14)
INCLUDEPICTURE"预习效果检测.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\预习效果检测.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\预习效果检测.tif" \* MERGEFORMATINET
1．平面上，到________的距离等于________的所有点组成的图形，叫做圆，这个________叫做圆心，这条________叫做圆的半径．
2．以点O为圆心的圆，记作“________”，读作“________”．
3．圆是轴对称图形，过圆心的每一条________都是它的对称轴．圆也是中心对称图形，________是它的对称中心．
4．与圆有关的概念：
(1)圆上任意两点间的线段叫做这个圆的一条________，如图，线段AC，AB；
(2)经过圆心的弦叫做这个圆的________，如图，线段AB；
(3)圆上任意两点间的部分叫做________，简称________，圆的直径将这个圆分成能够______的两条弧，这样的弧叫做________；
(4)大于半圆的弧叫做________，小于半圆的弧叫做________．以AB为端点的弧记作，读作“圆弧AB”或“弧AB”．
INCLUDEPICTURE"册80.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\册80.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\册80.tif" \* MERGEFORMATINET (第4题)　　INCLUDEPICTURE"册81.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\册81.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\册81.tif" \* MERGEFORMATINET (第6题)
5．能够________的两个圆叫做等圆．能够完全重合的两条弧叫做________．
6．图中有________条直径，________条弦，以A为一个端点的优弧有________条，劣弧有________条．
7．下列说法不正确的是(　　)
A．圆既是轴对称图形，又是中心对称图形
B．圆绕着它的圆心旋转任意角度，都能与自身重合
C．圆的对称轴有无数条，对称中心只有一个
D．圆的每一条直径都是它的对称轴
INCLUDEPICTURE"课堂导学.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\课堂导学.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\课堂导学.tif" \* MERGEFORMATINET
知识点1 圆的定义
INCLUDEPICTURE"L1.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\L1.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\L1.tif" \* MERGEFORMATINET 下列条件中，能确定一个圆的是(　　)
A．以点O为圆心
B．以2 cm长为半径
C．以点O为圆心，10 cm长为半径
D．经过点A
INCLUDEPICTURE"笔记.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\笔记.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\笔记.tif" \* MERGEFORMATINET
　　　　　　　　　　　　　　　
变式1如图，一只狗被拴在一个边长为3米的等边三角形建筑物的一角A处，绳长为6米，请用图形表示出狗能到达的区域．
INCLUDEPICTURE"册82.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\册82.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\册82.tif" \* MERGEFORMATINET
INCLUDEPICTURE"解.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\解.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\解.tif" \* MERGEFORMATINET
　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　知识点2 圆的对称性
INCLUDEPICTURE"L2.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\L2.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\L2.tif" \* MERGEFORMATINET 如图所示的三个圆是同心圆，那么图中阴影部分的面积为______．(结果保留π)
INCLUDEPICTURE"册83.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\册83.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\册83.tif" \* MERGEFORMATINET
　　　　　　　　　　　　　　　
变式2如图⊙A，⊙B，⊙C，两两不相交，且半径都是0.5 cm.则图中三个阴影扇形的弧长之和为(　　)
INCLUDEPICTURE"册84.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\册84.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\册84.tif" \* MERGEFORMATINET
A．π cm B. cm C. cm D. cm
知识点3 与圆有关的概念INCLUDEPICTURE"L3.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\L3.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\L3.tif" \* MERGEFORMATINET 下列命题中，正确的有(　　)
(1)直径是弦，但弦不一定是直径；
(2)半圆是弧，但弧不一定是半圆；
(3)半径相等且圆心不同的两个圆是等圆；
(4)一条弦把圆分成的两条弧中，至少有一条是优弧．
A．1个　　 B．2个　　 C．3个　　 D．4个
变式3－1如图，在⊙O中，点A，O，D和点B，O，C分别在一条直线上，图中共有______条弦，它们分别是____________．
INCLUDEPICTURE"册85.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\册85.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\册85.tif" \* MERGEFORMATINET (变式3－1)　　INCLUDEPICTURE"册86.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\册86.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\册86.tif" \* MERGEFORMATINET (变式3－2)
变式3－2如图，CD是⊙O的直径，E为⊙O上一点，∠EOD＝48°，A为DC延长线上一点，AE交⊙O于点B，且AB＝OC，则∠A的度数为________．
第二十八章　圆
28.1 圆的概念及性质
INCLUDEPICTURE"复习回顾.tif" INCLUDEPICTURE "复习回顾.tif" \* MERGEFORMAT INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\复习回顾.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\复习回顾.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\复习回顾.tif" \* MERGEFORMATINET
1．相等；相等；直径；半径　
2．62.8
INCLUDEPICTURE"预习效果.tif" INCLUDEPICTURE "预习效果.tif" \* MERGEFORMAT INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\预习效果.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\预习效果.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\预习效果.tif" \* MERGEFORMATINET
1．定点；定长；定点；定长　2.⊙O；圆O　3.直线；圆心
4．(1)弦　(2)直径
(3)圆弧；弧；完全重合；半圆
(4)优弧；劣弧
5．完全重合；等弧　
6．1；3；4；4　7.D
INCLUDEPICTURE"课堂导学.tif" INCLUDEPICTURE "课堂导学.tif" \* MERGEFORMAT INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\课堂导学.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\课堂导学.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\课堂导学.tif" \* MERGEFORMATINET
例1　C
变式1.解：如图，白色部分就是狗能到达的区域，阴影部分不能到达．
INCLUDEPICTURE"答103.tif" INCLUDEPICTURE "答103.tif" \* MERGEFORMAT INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\答103.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\答103.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\答103.tif" \* MERGEFORMATINET
例2　π　变式2.B　例3　C　
变式3－1. 3；AE，DC，AD
变式3－2.16°

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