在
中,
,
为
边上一点.
![](https://img.xkw.com/dksih/QBM/editorImg/2024/4/3/2b46ec7d-125d-4e40-a0a5-3ef6caa68748.png?resizew=186)
(1)用尺规完成作图:作线段
的垂直平分线交
于点
,交
于
,连接
,
;(注意:保留作图痕迹,不写作法,不下结论)
(2)若
,求证:
.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/047dc9795efa99b6fb9fdf9778085dab.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8455657dde27aabe6adb7b188e031c11.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/60ef95894ceebaf236170e8832dcf7e3.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2024/4/3/2b46ec7d-125d-4e40-a0a5-3ef6caa68748.png?resizew=186)
(1)用尺规完成作图:作线段
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0dc5c9827dfd0be5a9c85962d6ccbfb1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a0ed1ec316bc54c37c4286c208f55667.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/68a83fdd2ba72a2dba0b6b10bb3e06b9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e6e490f703eb6c9bb1278c78ebc2d661.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a438fe61c5d141d76d887b6fc2e8aaa7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/024dc2ccbbe321774df5d44e8785b203.png)
更新时间:2024-01-28 18:44:06
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【推荐1】如图,△ABC与△DCB中,AC与BD交于点E,且∠A=∠D,AB=DC
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【推荐2】如图,已知:在△AFD和△CEB中,点A、E、F、C在同一直线上,AE=CF,∠D=∠B,AD
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【推荐1】如图,在
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于M,交
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(2)若
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(1)若
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(2)若
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【推荐2】已知:如图,在
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【推荐1】(Ⅰ)已知点A与点B关于直线l成轴对称,请尺规作图作出直线l(保留作图痕迹);
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解答题-作图题
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【推荐2】如图,在平行四边形
中,
.用尺规完成以下基本作图:
![](https://img.xkw.com/dksih/QBM/2021/12/24/2879485419528192/2882962937110528/STEM/dca70cfc-3181-47bb-a9b3-0e06f5200d28.png?resizew=325)
(1)作
的平分线交
于点F.(保留作图痕迹,不写作法)
(2)在
上求作一点P,使点P到点C,点D的距离相等.
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8b9199a3de404cb13ae7710f73db5c8f.png)
![](https://img.xkw.com/dksih/QBM/2021/12/24/2879485419528192/2882962937110528/STEM/dca70cfc-3181-47bb-a9b3-0e06f5200d28.png?resizew=325)
(1)作
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/727ad3e630a224303d6d3b8ad5c114ba.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f52a58fbaf4fea03567e88a9f0f6e37e.png)
(2)在
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4cae70b8a9d2d2e96dea62c00ced04b9.png)
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【推荐1】如图,在
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【推荐2】教材呈现:(华师版九上28.3圆周角)半圆或直径所对的圆周角都相等,都等于90°(直角).
教材分析:如图,AB是⊙O的直径,∠C是AB所对的圆周角,则∠C=90°.如果我们把∠AOB看作是180°的圆心角,可以进一步得到的结论:∠C=
∠AOB,即:半圆所对的圆周角等于该半圆所对的圆心角的一半.
![](https://img.xkw.com/dksih/QBM/2022/2/9/2912601634586624/2914127945973760/STEM/699fc610-db03-413e-b25f-480c4f678e27.png?resizew=126)
联想猜测:那么对于非半圆所对的圆周角,是不是也有类似的规律呢?
探究化归:不难发现,按圆心与圆周角的位置关系分类,我们可将圆周角分为三类:
(1)圆心在圆周角的一条边(直径)上,如图①.
∵OA=OC,∴∠A=∠C.∴∠AOB=∠A+∠C=2∠C,∴∠C=
.
![](https://img.xkw.com/dksih/QBM/2022/2/9/2912601634586624/2914127945973760/STEM/55a92467-f8a6-4d94-b890-3850bcc7e1cf.png?resizew=383)
(2)圆心在圆周角内,如图②,我们将其化归为①的情形
由(1)的结论,∠1=
∠ ,∠2=
∠ .
∴∠ACB=∠1+∠2=
(∠ +∠ )=
∠ .
(3)圆心在圆周角外,如图③.显然我们也应将其化归为①的情形予以解决.请同学们在下面自己完成推理过程.
教材分析:如图,AB是⊙O的直径,∠C是AB所对的圆周角,则∠C=90°.如果我们把∠AOB看作是180°的圆心角,可以进一步得到的结论:∠C=
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f89eef3148f2d4d09379767b4af69132.png)
![](https://img.xkw.com/dksih/QBM/2022/2/9/2912601634586624/2914127945973760/STEM/699fc610-db03-413e-b25f-480c4f678e27.png?resizew=126)
联想猜测:那么对于非半圆所对的圆周角,是不是也有类似的规律呢?
探究化归:不难发现,按圆心与圆周角的位置关系分类,我们可将圆周角分为三类:
(1)圆心在圆周角的一条边(直径)上,如图①.
∵OA=OC,∴∠A=∠C.∴∠AOB=∠A+∠C=2∠C,∴∠C=
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f89eef3148f2d4d09379767b4af69132.png)
![](https://img.xkw.com/dksih/QBM/2022/2/9/2912601634586624/2914127945973760/STEM/55a92467-f8a6-4d94-b890-3850bcc7e1cf.png?resizew=383)
(2)圆心在圆周角内,如图②,我们将其化归为①的情形
由(1)的结论,∠1=
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f89eef3148f2d4d09379767b4af69132.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f89eef3148f2d4d09379767b4af69132.png)
∴∠ACB=∠1+∠2=
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f89eef3148f2d4d09379767b4af69132.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f89eef3148f2d4d09379767b4af69132.png)
(3)圆心在圆周角外,如图③.显然我们也应将其化归为①的情形予以解决.请同学们在下面自己完成推理过程.
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