【阅读】小明同学遇到这样一个问题:已知关于x的方程
(a、b、m为常数,
)的解是
,
,求方程
的解.他用“换元法”解决了这个问题.我们一起来看看小明同学的具体做法.
解:在方程
中令
,则方程可变形为
,
根据关于x的方程
的解是
,
,
可得方程
的解是
,
.
把
代入
得,
,把
代入
得,
,
所以方程
的解是
,
.
【理解】
已知关于x的一元二次方程
有两个实数根m,n.
(1)关于x的方程
的两根分别是______(用含有m、n的代数式表示);
(2)方程______的两个根分别是2m,2n.(答案不唯一,写出一个即可)
(3)【猜想与证明】
双察下表中每个方程的解的特点:
猜想:方程
的两个根与方程______的两个根互为倒数;
(4)仿照小明采用的“换元法”,证明你的猜想.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1852448a8b56a2ff23d1a797de43502e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/20849c00c47cbdc43f18d53341b6c4e5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d3e17ff0a5e5605747c4c6d9f7bb5165.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/204e5160ff110a19878e4fae639319e4.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/63e15c80d0056fac74953ad33db9d459.png)
解:在方程
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/63e15c80d0056fac74953ad33db9d459.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5ab466aedd6e176088d8dee7bc3e3aaa.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5943a50bdcd6b2702dfefa24ccf6e825.png)
根据关于x的方程
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1852448a8b56a2ff23d1a797de43502e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d3e17ff0a5e5605747c4c6d9f7bb5165.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/204e5160ff110a19878e4fae639319e4.png)
可得方程
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5943a50bdcd6b2702dfefa24ccf6e825.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ff983aae2b3ac77c054069665a9c8871.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bd2f96f8852882233cbb62e721a99755.png)
把
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/92002afa0b414eae387a91207c629398.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5ab466aedd6e176088d8dee7bc3e3aaa.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a089c207e39a24d0d82aa853ac2bbb8c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/107babba45f110012183dc4dc54490f7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5ab466aedd6e176088d8dee7bc3e3aaa.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9b384412acba251d87902ab928902f16.png)
所以方程
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/63e15c80d0056fac74953ad33db9d459.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b2639a322442997cb8685a5865d70c6c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7eba583e37243f3ba166bd1c11e58498.png)
【理解】
已知关于x的一元二次方程
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/807d62d0b5623b3bd3cb285560bf8436.png)
(1)关于x的方程
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c5a089ade14c227b4a07ccd1a578f5f.png)
(2)方程______的两个根分别是2m,2n.(答案不唯一,写出一个即可)
(3)【猜想与证明】
双察下表中每个方程的解的特点:
方程 | 方程的解 | 方程 | 方程的解 |
![]() | ![]() ![]() | ![]() | ![]() ![]() |
![]() | ![]() ![]() | ![]() | ![]() ![]() |
![]() | ![]() ![]() | ![]() | ![]() ![]() |
…… | …… | …… | …… |
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1f7b7abd6fa6d5e5ea052a8a537c7141.png)
(4)仿照小明采用的“换元法”,证明你的猜想.
21-22九年级上·江苏镇江·期末 查看更多[6]
江苏省镇江市2021-2022学年九年级上学期期末数学试题(已下线)第03讲 用一元二次方程解决问题-【暑假自学课】2022年新九年级数学暑假精品课(苏科版)(已下线)第02讲一元二次方程根与系数关系与解决问题(2大考点6种解题方法)-2022-2023学年九年级数学考试满分全攻略(苏科版)(已下线)专题2.17 换元法解一元二次方程(巩固篇)(专项练习)-2022-2023学年八年级数学下册基础知识专项讲练(浙教版)(已下线)专题17.17 换元法解一元二次方程(巩固篇)(专项练习)-2022-2023学年八年级数学下册基础知识专项讲练(沪科版)(已下线)第04讲一元二次方程的解法(因式分解法6种题型)-【暑假自学课】2023年新九年级数学暑假精品课(苏科版)
更新时间:2022-03-11 11:41:44
|
【知识点】 换元法解一元二次方程解读
相似题推荐
解答题-问答题
|
适中
(0.65)
解题方法
【推荐1】阅读下面解方程的过程:
解方程
.
设
,则原方程可化为
①,解得
,
.
当
时,
,解得
;当
时,
,解得
.
故原方程的解为
,
,
,
.
由方程得到①的过程,利用换元法达到简化方程的目的,体现了转化的数学思想.
解答下列问题:
(1)利用换元法解方程:
;
(2)
三边是
,
,
,若两直角边
,
满足
,斜边
,求
的面积.
解方程
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ac22e4c7b6910d461fe874a4825af1a5.png)
设
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e8da7c06be71acd821a73fadba4d1c35.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6d508887ede441f4d498565ceeb8682a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cda6ab0f37a6a39baffa6c98dc11dc16.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/aeb68f02e333c48c66a2656d5115cf46.png)
当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c50866229ec5a3640fb250f9bd2192b3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fbce8eb03871d4563436ddd3c2eb1808.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e2d442a230651549242b2b1ed35822c0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/de72a5190834f5dbe895596656c038b3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/35f227df33998c627b586997a32d8f62.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4ae8ef3413c0fa3e928e4a5b641d2b46.png)
故原方程的解为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e370d4caeeab628e65b82b0104114aad.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d8e9eb18f22ed5b7927a0d0bfa988bb0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/42cb565d4ee7a36e30865423e8524558.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a1c6765d414b74c91d0ad0f06db034a3.png)
由方程得到①的过程,利用换元法达到简化方程的目的,体现了转化的数学思想.
解答下列问题:
(1)利用换元法解方程:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/aaf474afc1a6f183153f39fb4da9e40c.png)
(2)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cfa8cee7d2463f6f7d352e8b65f47cf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c94bb12cee76221e13f9ef955b0aab1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/071a7e733d466949ac935b4b8ee8d183.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c94bb12cee76221e13f9ef955b0aab1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c7bfe5476882296af426480b7acd27e8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/60b97bb18e5ca34d22b5e827316a122a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cfa8cee7d2463f6f7d352e8b65f47cf3.png)
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解答题-问答题
|
适中
(0.65)
【推荐2】阅读:若
满足
,求
的值.
解:设
,
,则
,
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/353c64d906cfcd6b113a3d45b70d224b.png)
所以![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5afb1a80fe89331bfad0335f457f03cc.png)
请仿照上例解决下面的问题:
(1)若
满足
,求
的值.
(2)若
满足
,求
的值.
(3)如图,正方形
的边长为
,
,
,长方形
的面积是500,四边形
和
都是正方形,
是长方形,求图中阴影部分的面积(结果必须是一个具体的数值).
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/81dea63b8ce3e51adf66cf7b9982a248.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/59575e1b63e63c71e726d3d635206079.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f959467c3be51f6316491304a0890acd.png)
解:设
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a9d564c4460d15b315b1b45371df5e71.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7a7715e4bf5b2184682f4516662994db.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dd1fe64968786b15891af0e6befc42de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/353c64d906cfcd6b113a3d45b70d224b.png)
所以
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5afb1a80fe89331bfad0335f457f03cc.png)
请仿照上例解决下面的问题:
(1)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/81dea63b8ce3e51adf66cf7b9982a248.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3c571728f4e22c30be96835c4acaf2ac.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a5243e85aa726ebf2c43e76e9966727a.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/81dea63b8ce3e51adf66cf7b9982a248.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e450b038bdc4574bf7c0c08e1e4b0b72.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/872673432d988c1bd01e86b128d9c2d1.png)
(3)如图,正方形
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/81dea63b8ce3e51adf66cf7b9982a248.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f5d30cd3e53a9df24fe6da5e8a3a7ec5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8b5967bec6a3d3648b5bc59c12e492ae.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/24f515246d9ee093bfbf9983fd47357d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/060b114e21d0f6ff11b9391f9a77f3cf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fcd5e1e479972f2b5ec84cf00e85a9b2.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/013e00092604241a46e42342a8cb326c.png)
![](https://img.xkw.com/dksih/QBM/2019/9/5/2284058229661696/2284221791330304/STEM/e2cac908-711e-447d-b2ff-1df50a6fb84b.png?resizew=295)
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