Подстраница "Користувач:Галактион/Квадратне рівняння" создана для того, чтобы перенести информацию из раздела "Обговорення" статьи "Квадратне рівняння". Галактион 18:02, 5 березня 2010 (UTC)
Вот что должен знать абитуриент о квадратном уравнении
[ред. | ред. код]
Первая формула
![{\displaystyle ~(D<0\quad \to \quad (x\in \mathbb {R} \ \land \ ax^{2}+bx+c=0\quad \leftrightarrow \quad x\in \varnothing ))\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/ddea186eaafb2646140c31097df8f3c92d5676e7)
![{\displaystyle ~(D=0\quad \to \quad (x\in \mathbb {R} \ \land \ ax^{2}+bx+c=0\quad \leftrightarrow \quad x\in \{{\frac {-b}{2a}}\}))\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/e503fafd282329187e8fa68ba58beae741e2708f)
![{\displaystyle ~(D>0\quad \to \quad (x\in \mathbb {R} \ \ \land \ \ ax^{2}\ +\ bx\ +\ c=0\quad \leftrightarrow \quad x\in \{{\frac {-b-{\sqrt {D}}}{2a}},\quad {\frac {-b+{\sqrt {D}}}{2a}}\}))}](https://wikimedia.org/api/rest_v1/media/math/render/svg/0e4683b5365598349d6cf6aeac1f77f64414f8bf)
- Примечание
- 0.
![{\displaystyle ~\vdash \quad a\in \mathbb {R} \ \land \ b\in \mathbb {R} \ \land \ c\in \mathbb {R} \quad \leftrightarrow \ \{a,b,c\}\subseteq \mathbb {R} }](https://wikimedia.org/api/rest_v1/media/math/render/svg/04b0b6abeaf44c70c4b5bfe655e18b867ecda47d)
- 1.
![{\displaystyle ~\vdash \quad \{a,b,c\}\subseteq \mathbb {R} \ \land \ a\neq 0\ \land \ D=b^{2}-4ac\ \land \ D<0\quad \to }](https://wikimedia.org/api/rest_v1/media/math/render/svg/8863351fa28ee088bfa82cc32112201fa4ddf7f9)
![{\displaystyle ~(x\in \mathbb {C} \ \land \ ax^{2}+bx+c=0\quad \leftrightarrow \quad x\in \{{\frac {-b-{\sqrt {D}}}{2a}},\quad {\frac {-b+{\sqrt {D}}}{2a}}\}\ )}](https://wikimedia.org/api/rest_v1/media/math/render/svg/f97749e8dd4709d816d9647c56c74bd36ab9f94c)
- 2.
![{\displaystyle ~\vdash \quad x\in \{{\frac {-b}{2a}}\}\quad \leftrightarrow \quad x={\frac {-b}{2a}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/1c0845b3c6946551ec996f56a7da6ef48c3d1504)
- 3.
![{\displaystyle ~d\vdash \quad x_{1,2}={\frac {-b\pm {\sqrt {b^{2}-4ac}}}{2a}}\quad \leftrightarrow \quad x\in \{{\frac {-b-{\sqrt {b^{2}-4ac}}}{2a}},\quad {\frac {-b+{\sqrt {b^{2}-4ac}}}{2a}}\}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/b2aa26f7efe580a460ebc47662f2c25c9c886e6a)
- 4.
![{\displaystyle ~\vdash \quad x\in \{{\frac {-b-{\sqrt {b^{2}-4ac}}}{2a}},\quad {\frac {-b+{\sqrt {-b-4ac}}}{2a}}\}\quad \leftrightarrow }](https://wikimedia.org/api/rest_v1/media/math/render/svg/56a6ae8aa405407fd3ba0483530ab9f749058f38)
![{\displaystyle ~x={\frac {-b-{\sqrt {b^{2}-4ac}}}{2a}}\quad \lor \quad x={\frac {-b+{\sqrt {b^{2}-4ac}}}{2a}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/cbbc35b1cabc8a62d87535e71b4f158061c11fe9)
- 5. Руководствуясь предложениями (3) и (4), получаем
![{\displaystyle ~\vdash \quad x_{1,2}={\frac {-b\pm {\sqrt {b^{2}-4ac}}}{2a}}\quad \leftrightarrow \quad x={\frac {-b-{\sqrt {b^{2}-4ac}}}{2a}}\quad \lor \quad x={\frac {-b+{\sqrt {b^{2}-4ac}}}{2a}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/a078ec5aa4bda907a7c93523d1f479c2ebdba950)
Вторая формула
![{\displaystyle ~(D<0\quad \to \quad \{x|\ x\in \mathbb {R} \ \land \ ax^{2}+bx+c=0\}=\varnothing )\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/8ea0c63f5c56126988209f6ae866a42705eee987)
![{\displaystyle ~(D=0\quad \to \quad \{x|\ x\in \mathbb {R} \ \land \ ax^{2}+bx+c=0\}=\{{\frac {-b}{2a}}\})\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/d3fd7252e939a7acd4b79ce30275cd9a559e257f)
![{\displaystyle ~(D>0\quad \to \quad \{x|\ x\in \mathbb {R} \ \land \ ax^{2}+bx+c=0\}=\{{\frac {-b-{\sqrt {D}}}{2a}},\quad {\frac {-b+{\sqrt {D}}}{2a}}\})}](https://wikimedia.org/api/rest_v1/media/math/render/svg/36b0f1976da022dc9f5b59c9c10300744badf6de)
- Примечание
![{\displaystyle ~\{x|\ x\in \mathbb {C} \ \land \ ax^{2}+bx+c=0\}=\{{\frac {-b-{\sqrt {D}}}{2a}},\quad {\frac {-b+{\sqrt {D}}}{2a}}\}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/78b083c6ac7ad7fe1f6fc48d12cad721ed9a9b62)
Третья формула
![{\displaystyle ~(D<0\ \to \ \exists ^{\{0\}}x\ \ \ (x\in \mathbb {R} \ \land \ ax^{2}+bx+c=0)\ )\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/9649971543807ad32b3061c4ca460a4da8875a94)
![{\displaystyle ~(D\leq 0\ \to \ \exists ^{\{0,1\}}x\ (x\in \mathbb {R} \ \land \ ax^{2}+bx+c=0)\ )\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/1ce084077150908a001ad9f18acacb971351fc7d)
![{\displaystyle ~(D=0\ \to \ \exists ^{\{1\}}x\ \ \ (x\in \mathbb {R} \ \land \ ax^{2}+bx+c=0)\ )\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/a9145ec921c625a751478a656b300a48eecf8cac)
![{\displaystyle ~(D\geq 0\ \to \ \exists ^{\{1,2\}}x\ (x\in \mathbb {R} \ \land \ ax^{2}+bx+c=0)\ )\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/9a2dd65ecc9af6e922f6d4e9b3784dcaea84edf3)
![{\displaystyle ~(D>0\ \to \ \exists ^{\{2\}}x\ \ \ (x\in \mathbb {R} \ \land \ ax^{2}+bx+c=0)\ )}](https://wikimedia.org/api/rest_v1/media/math/render/svg/0072d18f8f23a43cf0a2a00b6d4b1fe3bf7fc098)
- Примечание
![{\displaystyle ~\exists ^{\{0\}}x\ (x\in \mathbb {R} \ \land \ ax^{2}+bx+c=0)\ \Leftrightarrow \ \forall x\ (x\in \mathbb {R} \to ax^{2}+bx+c\neq 0)}](https://wikimedia.org/api/rest_v1/media/math/render/svg/8616ced642ee58bdfe5792f1cee2ac74ac85013a)
Четвёртая формула
![{\displaystyle ~(D<0\ \to \ v\subseteq \varnothing )\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/4acc3d82dc64f1df6d1f30c9f5d9a5e909f082d2)
![{\displaystyle ~(D\leq 0\ \to \ \exists u\ (v\subseteq \{u\})\ )\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/3a238a875e2da226c3ff748e4a24b82affe1b191)
![{\displaystyle ~(D=0\ \to \ \exists u\ (v=\{u\})\ )\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/20ed548518b9601642e964be41441b62883809b3)
![{\displaystyle ~(D\geq 0\ \to \ \exists u\ (\{u\}\subseteq v)\quad \land \quad \exists u_{1}\exists u_{2}\ (u_{1}\neq u_{2}\ \land \ v\subseteq \{u_{1},u_{2}\})\ )\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/3e6e9f113a0ddf82088593cfc3d14cf8a1a2b962)
![{\displaystyle ~(D>0\ \to \ \exists u_{1}\exists u_{2}\ (u_{1}\neq u_{2}\ \land \ v=\{u_{1},u_{2}\})\ )}](https://wikimedia.org/api/rest_v1/media/math/render/svg/abb6300a862a2b8123695e20b2859e642ac14c9c)
Первая формула
![{\displaystyle ~(a>0\ \to \ \forall x\ (x\in \mathbb {R} \to ax^{2}+bx+c>0)\ )\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/1af3f1eb2d74967e6cea34a065a2d50b0059f373)
![{\displaystyle ~(a<0\ \to \ \forall x\ (x\in \mathbb {R} \to ax^{2}+bx+c<0)\ )}](https://wikimedia.org/api/rest_v1/media/math/render/svg/7cabcd0f6bc751f85b6d98c6e76172f95f79a393)
Вторая формула
![{\displaystyle ~(a>0\ \to \ \forall x\ (x\in \mathbb {R} \setminus \{{\frac {-b}{2a}}\}\ \to \ ax^{2}+bx+c>0)\ )\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/bd2bfd171267e8081c2280500877e4d74f1eeacd)
![{\displaystyle ~(a<0\ \to \ \forall x\ (x\in \mathbb {R} \setminus \{{\frac {-b}{2a}}\}\ \to \ ax^{2}+bx+c<0)}](https://wikimedia.org/api/rest_v1/media/math/render/svg/58e5be44bc77c89fc7434804d90566fa5ca428f5)
Третья формула
![{\displaystyle ~(a>0\ \to \ \forall x\ (x\in \mathbb {R} \ \land \ (x<{\frac {-b-{\sqrt {D}}}{2a}}\quad \lor \quad x>{\frac {-b+{\sqrt {D}}}{2a}})\ \to \ ax^{2}+bx+c>0)\ )\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/4784400d7cddb6bc0a3f041e8108b017e45aa849)
![{\displaystyle ~(a>0\ \to \ \forall x\ (x\in \mathbb {R} \ \land \ {\frac {-b-{\sqrt {D}}}{2a}}<x\ \land \ x<{\frac {-b+{\sqrt {D}}}{2a}}\ \to \ ax^{2}+bx+c<0)\ )\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/131858d84f5149411a9c854106c437ed745a5e2c)
![{\displaystyle ~(a<0\ \to \ \forall x\ (x\in \mathbb {R} \ \land \ (x<{\frac {-b-{\sqrt {D}}}{2a}}\quad \lor \quad x>{\frac {-b+{\sqrt {D}}}{2a}})\ \to \ ax^{2}+bx+c<0)\ )\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/e60df0c48c235319da1aad9141e854a165527a15)
![{\displaystyle ~(a<0\ \to \ \forall x\ (x\in \mathbb {R} \ \land \ {\frac {-b-{\sqrt {D}}}{2a}}<x\ \land \ x<{\frac {-b+{\sqrt {D}}}{2a}}\ \to \ ax^{2}+bx+c>0)\ )}](https://wikimedia.org/api/rest_v1/media/math/render/svg/0dd279aa6a3b1a8a667ffe213829614fa58a5550)
Кроме того, абитуриент должен знать следующее
[ред. | ред. код]
Первая формула
![{\displaystyle ~(a>0\ \to \ \forall x\ (x\in \mathbb {R} \setminus \{{\frac {-b}{2a}}\}\ \to \ f({\frac {-b}{2a}})<f(x)\ ))\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/f02a4cada12a35829518bc760deb0fdf6e1327fe)
![{\displaystyle ~(a<0\ \to \ \forall x\ (x\in \mathbb {R} \setminus \{{\frac {-b}{2a}}\}\ \to \ f({\frac {-b}{2a}})>f(x)\ ))}](https://wikimedia.org/api/rest_v1/media/math/render/svg/466070b93688ab1f77be8e069b2657511f47e3c1)
Вторая формула
![{\displaystyle ~(a>0\to \forall x_{1}\forall x_{2}\ (\{x_{1},x_{2}\}\subseteq \{x|\ x\in \mathbb {R} \ \land \ x\leq {\frac {-b}{2a}}\}\ \land \ x_{1}<x_{2}\to f(x_{1})>f(x_{2})\ ))\ \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/6430849021b7715ae5a3ec117ff8e96c54da4b25)
![{\displaystyle ~(a>0\to \forall x_{1}\forall x_{2}\ (\{x_{1},x_{2}\}\subseteq \{x|\ x\in \mathbb {R} \ \land \ x\geq {\frac {-b}{2a}}\}\ \land \ x_{1}<x_{2}\to f(x_{1})<f(x_{2})\ ))\ \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/0dcac2310c9766ce1a6d3b379107c27c9af0665d)
![{\displaystyle ~(a<0\to \forall x_{1}\forall x_{2}\ (\{x_{1},x_{2}\}\subseteq \{x|\ x\in \mathbb {R} \ \land \ x\leq {\frac {-b}{2a}}\}\ \land \ x_{1}<x_{2}\to f(x_{1})<f(x_{2})\ ))\ \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/3584fae5dd46d8cd50eb2e81ce9aea9d325d2da0)
![{\displaystyle ~(a<0\to \forall x_{1}\forall x_{2}\ (\{x_{1},x_{2}\}\subseteq \{x|\ x\in \mathbb {R} \ \land \ x\geq {\frac {-b}{2a}}\}\ \land \ x_{1}<x_{2}\to f(x_{1})>f(x_{2})\ ))}](https://wikimedia.org/api/rest_v1/media/math/render/svg/0247618a843dc139baede02f572c8de7f78117e3)
Третья формула
![{\displaystyle ~(a>0\ \to \ \forall x_{1}\forall x_{2}\ (\{x_{1},x_{2}\}\subseteq \mathbb {R} \ \land \ x_{1}\neq \ x_{2}\ \to \ f({\frac {x_{1}+x_{2}}{2}})<{\frac {f(x_{1})+f(x_{2})}{2}}))\quad \land }](https://wikimedia.org/api/rest_v1/media/math/render/svg/20897c95e39c6f814a33a0d2baf84d03d8a677fe)
![{\displaystyle ~(a<0\ \to \ \forall x_{1}\forall x_{2}\ (\{x_{1},x_{2}\}\subseteq \mathbb {R} \ \land \ x_{1}\neq x_{2}\ \to \ f({\frac {x_{1}+x_{2}}{2}})>{\frac {f(x_{1})+f(x_{2})}{2}}))}](https://wikimedia.org/api/rest_v1/media/math/render/svg/3cd6fa1cf5868aca3f2b3a8c078972adaef41b4a)
--Галактион 14:43, 17 травня 2009 (UTC)
- А чому у вас тільки дійсні коефіцієнти? --Олюсь 18:54, 17 травня 2009 (UTC)
- Я предположил, что в Украинских школах рассматриваются квадратные уравнения с вещественными коэффициентами. Если я ошибся, тогда добавьте, пожалуйста, сведения о решениях квадратного уравнения с комплексными коэффициетами. --Галактион 21:05, 17 травня 2009 (UTC)