java - 二次方程求解器无法在 Java 中获得结果

Question

我的代码本应求解二次方程，但结果产生了 NaN。

我已经四处寻找了 2 天，但找不到解决方案。任何和所有建议将不胜感激!

package quadratic;

import java.util.Scanner;

public class Formlua {

    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);
        System.out.println("enter value of A ");
        double a = input.nextDouble();
        System.out.println("enter value of B ");
        double b = input.nextDouble();
        System.out.println("enter value of C ");    
        double c = input.nextDouble();
        double four = 4;
        double square = Math.sqrt(b* b - 4 * a * c );

        double root1 = (-b + square) / (2*a);

        double root2 = (-b - square) / (2*a);   
        System.out.println("The answer is " + root1 + "and" + root2);

        System.out.println("Do you want to continue? y/n");

        String user = input.toString();
        if(user.equalsIgnoreCase("y"));
    }
}

Answer 1

这段代码:

Math.sqrt(b* b - 4 * a * c );

可能导致 NaN(“不是数字”)。

如果b* b - 4 * a * c的值为负数，则只有复数有解(double数据类型没有)

应该有一个条件

if (b* b - 4 * a * c<0) {
    System.out.println("There is no solution in real numbers");
    return;
}