C++ 实例 - 求一元二次方程的根

二次方程 ax²+bx+c = 0 (其中a≠0），a 是二次项系数，bx 叫作一次项，b是一次项系数；c叫作常数项。

x 的值为：

根的判别式

实例

#include <bits/stdc++.h>
using namespace std;
 
int main() {
 
    float a, b, c, x1, x2, discriminant, realPart, imaginaryPart;
    // 输入 a, b 和 c
    cin >> a >> b >> c;
    discriminant = b * b - 4 * a * c;
    
    if (discriminant > 0) {
        x1 = (-b + sqrt(discriminant)) / (2 * a);
        x2 = (-b - sqrt(discriminant)) / (2 * a);
        cout << "Roots are real and different." << endl;
        cout << "x1 = " << x1 << endl;
        cout << "x2 = " << x2 << endl;
    } else if (discriminant == 0) {
        cout << "实根相同：" << endl;
        x1 = (-b + sqrt(discriminant)) / (2 * a);
        cout << "x1 = x2 =" << x1 << endl;
    } else {
        realPart = -b/(2 * a);
        imaginaryPart =sqrt(-discriminant)/(2 * a);
        cout << "实根不同："  << endl;
        cout << "x1 = " << realPart << "+" << imaginaryPart << "i" << endl;
        cout << "x2 = " << realPart << "-" << imaginaryPart << "i" << endl;
    }
 
    return 0;
}

以上程序执行输出结果为：

4 5 1
实根不同：
x1 = -0.25
x2 = -1