浙教版九上数学课本第24页例1:如图1窗户边框的上部分是由4个全等扇形组成的半圆,下部分是矩形.如果制作一个窗户边框的材料总长度为
,那么如何设计这个窗户边框的尺寸,使透光面积最大?这道例题的答案是:当窗户半圆的半径约为
时,透光面积最大约为
.
我们如果改变这个窗户的形状,上部改为一个等边三角形(如图2),材料总长度仍为
,利用图2,解答下列问题:
时,求此时窗户的透光面积;
(2)与课本中例1比较,改变窗户形状后,窗户的透光面积的最大值是否变大?通过计算说明.(
取
)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9e17ee14bd91bfff409c06fd434f6745.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2586d886c81a00c19bbca6bd21d09e36.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/aeb737739252e26ff063f66d9c32c592.png)
我们如果改变这个窗户的形状,上部改为一个等边三角形(如图2),材料总长度仍为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9e17ee14bd91bfff409c06fd434f6745.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c01b4e82dc80021c9cfceeda4fd67992.png)
(2)与课本中例1比较,改变窗户形状后,窗户的透光面积的最大值是否变大?通过计算说明.(
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a7ffe8515ff6183c1c7775dc6f94bdb8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f8a2e29cebeaca8f07a31ff8ed725880.png)
更新时间:2024-02-21 18:32:29
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【推荐1】直线l过点A(a,0)和点B(0,b),其中a>0,b>0,若a+b=12,点O为原点,△AOB的面积为S,则当b为何值时,S取得最大值?并求出这个最大值.
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【推荐2】如图,抛物线
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轴交于点
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(1)求此抛物线的表达式;
(2)点
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轴上,直线
将
面积分成
两部分,直线
与
交于点
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dad2a36927223bd70f426ba06aea4b45.png)
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【推荐1】在△ABC中,AB、AC边的垂直平分线分别交BC边于点M、N.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/8/6/1df99936-b48b-4add-9978-2688a7e349ae.png?resizew=668)
(1)如图①,若△AMN是等边三角形,则∠BAC= °;
(2)如图②,若∠BAC=135°,求证:BM2+CN2=MN2
(3)如图③,∠ABC的平分线BP和AC边的垂直平分线相交于点P,过点P作PH垂直BA的延长线于点H.若AB=4,CB=9,求AH的长.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/8/6/1df99936-b48b-4add-9978-2688a7e349ae.png?resizew=668)
(1)如图①,若△AMN是等边三角形,则∠BAC= °;
(2)如图②,若∠BAC=135°,求证:BM2+CN2=MN2
(3)如图③,∠ABC的平分线BP和AC边的垂直平分线相交于点P,过点P作PH垂直BA的延长线于点H.若AB=4,CB=9,求AH的长.
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【推荐2】如图1,和
都是等边三角形.
(1)求证:
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(2)若
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(3)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/32e4b3716628ee426bc145f59b8cedef.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
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【推荐1】如图,在矩形ABCD的边AB上取一点E,连接CE并延长和DA的延长线交于点G,过点E作CG的垂线与CD的延长线交于点H,与DG交于点F,连接GH.
![](https://img.xkw.com/dksih/QBM/2020/8/12/2526404023517184/2526527509086208/STEM/39088bdd0cdf43ff942c10f2032d4a74.png?resizew=206)
(1)当tan∠BEC=2且BC=4时,求CH的长;
(2)求证:DF•FG=HF•EF;
(3)连接DE,求证:∠CDE=∠CGH.
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(2)求证:DF•FG=HF•EF;
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【推荐2】如图,在平行四边形
中,
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交
于点E,
交
于点F,交
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的形状,并说明理由.
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