2次方程式や3次方程式の解と係数の間には、実はとても便利な関係があるんだ。この関係を理解すると、複雑な計算をしなくても解の和や積を簡単に求められるようになる。
算数51 views·Updated May 26, 2026·1 page解と係数の関係を学ぼう
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解と係数の関係
解と係数の関係は、方程式の解を直接求めなくても、解同士の和や積が分かってしまう超便利な公式だ。テストでも頻出だから、しっかりマスターしよう。
2次方程式 ax² + bx + c = 0 の2つの解をα、βとすると：
- 解の和：α + β = -b/a
- 解の積：αβ = c/a
3次方程式 ax³ + bx² + cx + d = 0 の3つの解をα、β、γとすると：
- α + β + γ = -b/a
- αβ + βγ + γα = c/a
- αβγ = -d/a
💡 ポイント！ 係数の符号に注意！解の和は常に最高次の項の次の係数に-1をかけて最高次の係数で割ったものだよ。
この公式を覚えておけば、解の値が分数や無理数になる複雑な方程式でも、解の和や積をパッと計算できる。計算ミスも減らせるから一石二鳥だね。
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算数51 views·Updated May 26, 2026·1 page解と係数の関係を学ぼう
2次方程式や3次方程式の解と係数の間には、実はとても便利な関係があるんだ。この関係を理解すると、複雑な計算をしなくても解の和や積を簡単に求められるようになる。
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解と係数の関係
解と係数の関係は、方程式の解を直接求めなくても、解同士の和や積が分かってしまう超便利な公式だ。テストでも頻出だから、しっかりマスターしよう。
2次方程式 ax² + bx + c = 0 の2つの解をα、βとすると：
- 解の和：α + β = -b/a
- 解の積：αβ = c/a
3次方程式 ax³ + bx² + cx + d = 0 の3つの解をα、β、γとすると：
- α + β + γ = -b/a
- αβ + βγ + γα = c/a
- αβγ = -d/a
💡 ポイント！ 係数の符号に注意！解の和は常に最高次の項の次の係数に-1をかけて最高次の係数で割ったものだよ。
この公式を覚えておけば、解の値が分数や無理数になる複雑な方程式でも、解の和や積をパッと計算できる。計算ミスも減らせるから一石二鳥だね。
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
Where can I download the Knowunity app?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
Most popular content in 算数
6Most popular content
9Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.6/5App Store
4.7/5Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan SiOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha KlichAndroid user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
AnnaiOS user