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第二十八章　圓
28.1 圓的概念及性質(zhì)
INCLUDEPICTURE"復(fù)習(xí)回顧.tif" INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\復(fù)習(xí)回顧.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\復(fù)習(xí)回顧.tif" \* MERGEFORMATINET
1．在同一個圓里，所有的半徑都________，所有的直徑都________，且________是________的2倍．
2．有一個圓形花池的半徑是10米，如果繞其周圍走一圈，至少需要走_(dá)_______米．(π取3.14)
INCLUDEPICTURE"預(yù)習(xí)效果檢測.tif" INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\預(yù)習(xí)效果檢測.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\預(yù)習(xí)效果檢測.tif" \* MERGEFORMATINET
1．平面上，到________的距離等于________的所有點(diǎn)組成的圖形，叫做圓，這個________叫做圓心，這條________叫做圓的半徑．
2．以點(diǎn)O為圓心的圓，記作“________”，讀作“________”．
3．圓是軸對稱圖形，過圓心的每一條________都是它的對稱軸．圓也是中心對稱圖形，________是它的對稱中心．
4．與圓有關(guān)的概念：
(1)圓上任意兩點(diǎn)間的線段叫做這個圓的一條________，如圖，線段AC，AB；
(2)經(jīng)過圓心的弦叫做這個圓的________，如圖，線段AB；
(3)圓上任意兩點(diǎn)間的部分叫做________，簡稱________，圓的直徑將這個圓分成能夠______的兩條弧，這樣的弧叫做________；
(4)大于半圓的弧叫做________，小于半圓的弧叫做________．以AB為端點(diǎn)的弧記作，讀作“圓弧AB”或“弧AB”．
INCLUDEPICTURE"冊80.tif" INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\冊80.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\冊80.tif" \* MERGEFORMATINET (第4題)　　INCLUDEPICTURE"冊81.tif" INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\冊81.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\冊81.tif" \* MERGEFORMATINET (第6題)
5．能夠________的兩個圓叫做等圓．能夠完全重合的兩條弧叫做________．
6．圖中有________條直徑，________條弦，以A為一個端點(diǎn)的優(yōu)弧有________條，劣弧有________條．
7．下列說法不正確的是(　　)
A．圓既是軸對稱圖形，又是中心對稱圖形
B．圓繞著它的圓心旋轉(zhuǎn)任意角度，都能與自身重合
C．圓的對稱軸有無數(shù)條，對稱中心只有一個
D．圓的每一條直徑都是它的對稱軸
INCLUDEPICTURE"課堂導(dǎo)學(xué).tif" INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\課堂導(dǎo)學(xué).tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\課堂導(dǎo)學(xué).tif" \* MERGEFORMATINET
知識點(diǎn)1 圓的定義
INCLUDEPICTURE"L1.tif" INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\L1.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\L1.tif" \* MERGEFORMATINET 下列條件中，能確定一個圓的是(　　)
A．以點(diǎn)O為圓心
B．以2 cm長為半徑
C．以點(diǎn)O為圓心，10 cm長為半徑
D．經(jīng)過點(diǎn)A
INCLUDEPICTURE"筆記.tif" INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\筆記.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\筆記.tif" \* MERGEFORMATINET
　　　　　　　　　　　　　　　
變式1如圖，一只狗被拴在一個邊長為3米的等邊三角形建筑物的一角A處，繩長為6米，請用圖形表示出狗能到達(dá)的區(qū)域．
INCLUDEPICTURE"冊82.tif" INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\冊82.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\冊82.tif" \* MERGEFORMATINET
INCLUDEPICTURE"解.tif" INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\解.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\解.tif" \* MERGEFORMATINET
　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　知識點(diǎn)2 圓的對稱性
INCLUDEPICTURE"L2.tif" INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\L2.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\L2.tif" \* MERGEFORMATINET 如圖所示的三個圓是同心圓，那么圖中陰影部分的面積為______．(結(jié)果保留π)
INCLUDEPICTURE"冊83.tif" INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\冊83.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\冊83.tif" \* MERGEFORMATINET
　　　　　　　　　　　　　　　
變式2如圖⊙A，⊙B，⊙C，兩兩不相交，且半徑都是0.5 cm.則圖中三個陰影扇形的弧長之和為(　　)
INCLUDEPICTURE"冊84.tif" INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\冊84.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\冊84.tif" \* MERGEFORMATINET
A．π cm B. cm C. cm D. cm
知識點(diǎn)3 與圓有關(guān)的概念I(lǐng)NCLUDEPICTURE"L3.tif" INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\L3.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\L3.tif" \* MERGEFORMATINET 下列命題中，正確的有(　　)
(1)直徑是弦，但弦不一定是直徑；
(2)半圓是弧，但弧不一定是半圓；
(3)半徑相等且圓心不同的兩個圓是等圓；
(4)一條弦把圓分成的兩條弧中，至少有一條是優(yōu)弧．
A．1個　　 B．2個　　 C．3個　　 D．4個
變式3－1如圖，在⊙O中，點(diǎn)A，O，D和點(diǎn)B，O，C分別在一條直線上，圖中共有______條弦，它們分別是____________．
INCLUDEPICTURE"冊85.tif" INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\冊85.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\冊85.tif" \* MERGEFORMATINET (變式3－1)　　INCLUDEPICTURE"冊86.tif" INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\冊86.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\冊86.tif" \* MERGEFORMATINET (變式3－2)
變式3－2如圖，CD是⊙O的直徑，E為⊙O上一點(diǎn)，∠EOD＝48°，A為DC延長線上一點(diǎn)，AE交⊙O于點(diǎn)B，且AB＝OC，則∠A的度數(shù)為________．
第二十八章　圓
28.1 圓的概念及性質(zhì)
INCLUDEPICTURE"復(fù)習(xí)回顧.tif" INCLUDEPICTURE "復(fù)習(xí)回顧.tif" \* MERGEFORMAT INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\復(fù)習(xí)回顧.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\復(fù)習(xí)回顧.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\復(fù)習(xí)回顧.tif" \* MERGEFORMATINET
1．相等；相等；直徑；半徑　
2．62.8
INCLUDEPICTURE"預(yù)習(xí)效果.tif" INCLUDEPICTURE "預(yù)習(xí)效果.tif" \* MERGEFORMAT INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\預(yù)習(xí)效果.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\預(yù)習(xí)效果.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\預(yù)習(xí)效果.tif" \* MERGEFORMATINET
1．定點(diǎn)；定長；定點(diǎn)；定長　2.⊙O；圓O　3.直線；圓心
4．(1)弦　(2)直徑
(3)圓弧；弧；完全重合；半圓
(4)優(yōu)弧；劣弧
5．完全重合；等弧　
6．1；3；4；4　7.D
INCLUDEPICTURE"課堂導(dǎo)學(xué).tif" INCLUDEPICTURE "課堂導(dǎo)學(xué).tif" \* MERGEFORMAT INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\課堂導(dǎo)學(xué).tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\課堂導(dǎo)學(xué).tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\課堂導(dǎo)學(xué).tif" \* MERGEFORMATINET
例1　C
變式1.解：如圖，白色部分就是狗能到達(dá)的區(qū)域，陰影部分不能到達(dá)．
INCLUDEPICTURE"答103.tif" INCLUDEPICTURE "答103.tif" \* MERGEFORMAT INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\答103.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\答103.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\課件\\九數(shù)JJ河北（北京）\\答103.tif" \* MERGEFORMATINET
例2　π　變式2.B　例3　C　
變式3－1. 3；AE，DC，AD
變式3－2.16°

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