1 . 15(几何证明选讲选做题)如图,
是圆
的直径,
,
,则![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cfd41df221293d5cdbab35be6ae5987e.png)
______
![](https://img.xkw.com/dksih/QBM/2015/10/8/1572247535755264/1572247541481472/STEM/6dd94026e36a43a1b1eb042f9fe3dfca.png?resizew=27)
![](https://img.xkw.com/dksih/QBM/2015/10/8/1572247535755264/1572247541481472/STEM/03fd77017d714b17b8152e4a47c614e2.png?resizew=16)
![](https://img.xkw.com/dksih/QBM/2015/10/8/1572247535755264/1572247541481472/STEM/797c984e40ed4074a9de99b557e9f1cc.png?resizew=68)
![](https://img.xkw.com/dksih/QBM/2015/10/8/1572247535755264/1572247541481472/STEM/8021a76cfd17480ba5e4d7239a7419a5.png?resizew=103)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cfd41df221293d5cdbab35be6ae5987e.png)
![](https://img.xkw.com/dksih/QBM/2015/10/8/1572247535755264/1572247541481472/STEM/0a2644f1caf54e728fc07e6dbfcc6136.png?resizew=121)
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2 . 如图,延长△ABC的角平分线AD交其外接圆于E,若AD =AB= 1,DE =
,则AC=_________ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cf298f00799cbf34b4db26f5f63af92f.png)
![](https://img.xkw.com/dksih/QBM/2015/6/16/1572126201487360/1572126207524864/STEM/460448641459437db3c1fec97ab5ba10.png?resizew=144)
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3 . (几何证明选讲选做题)如图,PA与圆
相切于A,PCB为圆
的割线,并且不过圆心
,已知
,
,
,则圆
的半径等于__________ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1dde8112e8eb968fd042418dd632759e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1dde8112e8eb968fd042418dd632759e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1dde8112e8eb968fd042418dd632759e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ba8a127b3fc5dc9e8b4f902adb54ad7f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/967f74b8993c61634ceed95edca05ffd.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b5064f5ce5ac8428e277fd578da84ec6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1dde8112e8eb968fd042418dd632759e.png)
![](https://img.xkw.com/dksih/QBM/2015/5/13/1572103208280064/1572103214129152/STEM/d6528b5aa76b436a85f2e95aee72be56.png?resizew=205)
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