Use java to solve triangle angle problems

Triangle angle formula:

From the above formula we can see that to calculate the angle, we must know the side length, So how do we calculate the side length?

First we need to know the coordinates of the three vertices, and then calculate the distance between points.

Code:

package com.zhuo.base.com.zhuo.base;

import java.util.Scanner;

public class ComputeAngles {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        //提示用户输入三个点
        System.out.print("Enter three points:");
        double x1 = input.nextDouble();
        double y1 = input.nextDouble();
        double x2 = input.nextDouble();
        double y2 = input.nextDouble();
        double x3 = input.nextDouble();
        double y3 = input.nextDouble();
        //计算三条边
        double a = Math.sqrt((x2 - x3) * (x2 - x3) + (y2 - y3) * (y2- y3));
        double b = Math.sqrt((x1 - x3) * (x1 - x3) + (y1 - y3) * (y1 - y3));
        double c = Math.sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
        //计算三个角
        double A = Math.toDegrees(Math.acos((a * a - b * b - c * c) / (-2 * b * c)));
        double B = Math.toDegrees(Math.acos((b * b - a * a - c * c) / (-2 * a * c)));
        double C = Math.toDegrees(Math.acos((c * c - a * a - b * b) / (-2 * a * b)));
        //显示结果，保留小数点后两位
        System.out.println("The three angles are " +
                Math.round(A * 100) / 100.0 + " " +
                Math.round(B * 100) / 100.0 + " " +
                Math.round(C * 100) / 100.0);
    }
}

Result display:

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