如图,AD与BC交于点O,①AD=BC;②∠A=∠C;③AB=CD,请以①②③中的两个作为条件,另一个为结论,写出一个真命题,并加以证明.
已知:
求证:
证明:
已知:
求证:
证明:
更新时间:2021-08-01 10:48:06
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【推荐1】如图,在△ABC中,∠ACB=90°,AC=BC,D是AB边上一点(点D与A,B不重合),连结CD,将线段CD绕点C按逆时针方向旋转90°得到线段CE,连结DE交BC于点F,连接BE.
(1)求证:EB⊥AB;
(2)当AD=BF时,求∠BEF的度数.
(1)求证:EB⊥AB;
(2)当AD=BF时,求∠BEF的度数.
![](https://img.xkw.com/dksih/QBM/2021/10/28/2839275168186368/2842827609710592/STEM/ada3b7c1b6fb4e8cabb87766758aa969.png?resizew=154)
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解答题-证明题
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【推荐2】如图,
,
,
,点
在
的延长线上,连接
.
![](https://img.xkw.com/dksih/QBM/2020/9/29/2560007066705920/2563327620341760/STEM/7e4d4291ade94c4b914ecb29d796c77e.png?resizew=230)
(1)①求证:
;②求
的度数;
(2)当
时,请直接写出
的度数.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/047dc9795efa99b6fb9fdf9778085dab.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e2d212c1709b8e72a055cf1b5381ef64.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/738592f7fdb4bddb03a187776f98a4c9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8455657dde27aabe6adb7b188e031c11.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0dc5c9827dfd0be5a9c85962d6ccbfb1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1fc56c77464a17a1e97b568762a3e2c6.png)
![](https://img.xkw.com/dksih/QBM/2020/9/29/2560007066705920/2563327620341760/STEM/7e4d4291ade94c4b914ecb29d796c77e.png?resizew=230)
(1)①求证:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/421291381be28da4bd16560fd383b4a9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c3db3f03c05b28155f9c0d31abfab198.png)
(2)当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/28b2c767972aa7c8ca26d50d33bc001b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c3db3f03c05b28155f9c0d31abfab198.png)
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【推荐1】【阅读理解】
如果把一个命题(记作
)的题设和结论交换位置,得到另一个命题(记作
),那么这两个命题叫做互逆命题,其中命题
称为原命题,命题
称为原命题的逆命题.
例如:原命题“对顶角相等”的逆命题为“相等的角是对顶角”.
【解决问题】
给出命题
“如果
,那么
.”
(1)写出命题
的题设和结论,及逆命题
.
(2)判断命题
是真命题还是假命题,若是假命题,请举出一个反例进行说明.
如果把一个命题(记作
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b1010846eeec6c9da29640f5aa3f8738.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9aa8a716a31b0f51b70fdf9bdb257909.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b1010846eeec6c9da29640f5aa3f8738.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9aa8a716a31b0f51b70fdf9bdb257909.png)
例如:原命题“对顶角相等”的逆命题为“相等的角是对顶角”.
【解决问题】
给出命题
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/51441c8788ff11be766766227793246d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1f22fec5a381ae8aca93d876e54c79de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/421a473589d5abdd504fdb110828611a.png)
(1)写出命题
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b1010846eeec6c9da29640f5aa3f8738.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9aa8a716a31b0f51b70fdf9bdb257909.png)
(2)判断命题
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9aa8a716a31b0f51b70fdf9bdb257909.png)
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【推荐2】【发现】
①![](https://staticzujuan.xkw.com/quesimg/Upload/formula/882f9eb8f6a0546e669297b7af725c92.png)
②![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b4ba992cb7aeb8d1fea1a06cbf33ff09.png)
③![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5cd9bf38ba7aab964aa5c73fdd5b0b54.png)
④
……
(1)根据上述等式反映的规律,请再写出一个等式:______.
【归纳】等式①,②,③,④,所反映的规律,可归纳为一个真命题:
对于任意两个有理数a,b,若______,则
;反之也成立.
【应用】根据上述所归纳的真命题,解决下列问题:
(2)若
与
的值互为相反数,则
______;
(3)若
与
的值互为相反数,且
,求a的值.
①
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/882f9eb8f6a0546e669297b7af725c92.png)
②
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b4ba992cb7aeb8d1fea1a06cbf33ff09.png)
③
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5cd9bf38ba7aab964aa5c73fdd5b0b54.png)
④
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f805d2410debc99144d161c3827548d8.png)
(1)根据上述等式反映的规律,请再写出一个等式:______.
【归纳】等式①,②,③,④,所反映的规律,可归纳为一个真命题:
对于任意两个有理数a,b,若______,则
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fbd65171f7c62ffc38d1e0b77613a069.png)
【应用】根据上述所归纳的真命题,解决下列问题:
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3a177fe47b42e26dc773d8972f6af8a6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e06602a0d9f477d28d57227205e8117d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2d2e01d7905ab771f63901a98c9ef276.png)
(3)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9b14c150cc5028650378946c1fff7939.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a075312a35675ffe80b38d19665925f3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ecda9594c73beacb44f225cc9ba28af7.png)
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