ComputeAngles.java

import java.util.Scanner;

/**
 * Created by Melissa on 18/04/2017.
 */
public class ComputeAngles {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        // Prompt the user to enter three points
        System.out.print("Enter the coordinates of three points separated by spaces like x1 y1 x2 y2 x3 y3: ");
        double x1 = input.nextDouble();
        double y1 = input.nextDouble();
        double x2 = input.nextDouble();
        double y2 = input.nextDouble();
        double x3 = input.nextDouble();
        double y3 = input.nextDouble();

        // Compute three sides
        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));

        // Compute three angles
        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 - b * b - a * a) / (-2 * a * b)));

        // Display results
        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);
    }
}