如图,在锐角三角形纸片ABC中,AC>BC,点D,E,F分别在边AB,BC,CA上.
![](https://img.xkw.com/dksih/QBM/2015/9/9/1573910794108928/1573910800187392/STEM/b4f01aab885743b0b7a71f506d4cbb58.png)
(1)已知:DE∥AC,DF∥BC.
①判断
四边形DECF一定是什么形状?
②裁剪
当AC=24cm,BC=20cm,∠ACB=45°时,请你探索:如何剪四边形DECF,能使它的面积最大,并证明你的结论;
(2)折叠
请你只用两次折叠,确定四边形的顶点D,E,C,F,使它恰好为菱形,并说明你的折法和理由.
![](https://img.xkw.com/dksih/QBM/2015/9/9/1573910794108928/1573910800187392/STEM/b4f01aab885743b0b7a71f506d4cbb58.png)
(1)已知:DE∥AC,DF∥BC.
①判断
四边形DECF一定是什么形状?
②裁剪
当AC=24cm,BC=20cm,∠ACB=45°时,请你探索:如何剪四边形DECF,能使它的面积最大,并证明你的结论;
(2)折叠
请你只用两次折叠,确定四边形的顶点D,E,C,F,使它恰好为菱形,并说明你的折法和理由.
更新时间:2016-12-06 02:32:37
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【知识点】 相似三角形的判定与性质综合
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【推荐2】如图,抛物线
与
轴交于
,
,
两点(点
在点
的左侧),与
轴交于点
,且
,
的平分线
交
轴于点
,过点
且垂直于
的直线
交
轴于点
,点
是
轴下方抛物线上的一个动点,过点
作
轴,垂足为
,交直线
于点
.
(1)求抛物线的解析式;
(2)设点
的横坐标为
,当
时,求
的值;
(3)当直线
为抛物线的对称轴时,以点
为圆心,
为半径作
,点
为
上的一个动点,求
的最小值.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c83f2638d71e5d00c241c6704b32094d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/81dea63b8ce3e51adf66cf7b9982a248.png)
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7f9e8449aad35c5d840a3395ea86df6d.png)
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(1)求抛物线的解析式;
(2)设点
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dad2a36927223bd70f426ba06aea4b45.png)
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