Chapter 2 Question 2.19, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

(Geometry: area of a triangle) Write a program that prompts the user to enter three points (x1, y1), (x2, y2), (x3, y3) of a triangle and displays its area. The formula for computing the area of a triangle is 

s = (side1 + side2 + side3)/2; 

area = √2s(s - side1)(s - side2)(s - side3) Here is a sample run:

Solution

/*

(Geometry: area of a triangle) Write a program that prompts the user to enter

three points (x1, y1), (x2, y2), (x3, y3) of a triangle and displays its area.

*/

import java.util.Scanner;

public class Exercise_02_19

{

    public static void main(String[] args)

    {

        Scanner input = new Scanner(System.in);

        // Prompt the user to enter three points

        System.out.print("Enter x1 point for a triangle: ");

        double x1 = input.nextDouble();

        System.out.print("Enter y1 point for a triangle: ");

        double y1 = input.nextDouble();

System.out.print("Enter x2 point for a triangle: ");

        double x2 = input.nextDouble();

System.out.print("Enter y2 point for a triangle: ");

        double y2 = input.nextDouble();

System.out.print("Enter x3 point for a triangle: ");

        double x3 = input.nextDouble();

System.out.print("Enter y3 point for a triangle: ");

        double y3 = input.nextDouble();

        // Compute the area of a triangle

        double side1 = Math.pow(Math.pow(x2 - x1, 2) + Math.pow(y2 - y1, 2), 0.5);

        double side2 = Math.pow(Math.pow(x3 - x2, 2) + Math.pow(y3 - y2, 2), 0.5);

        double side3 = Math.pow(Math.pow(x1 - x3, 2) + Math.pow(y1 - y3, 2), 0.5);

        double s = (side1 + side2 + side3) / 2;

        double area = Math.pow(s * (s - side1) * (s - side2) * (s - side3), 0.5);

        // Display result

        System.out.println("The area of the triangle is " + area);

    }

}

Output

Enter x1 point for a triangle: 12.5

Enter y1 point for a triangle: 13.6

Enter x2 point for a triangle: 18.6

Enter y2 point for a triangle: 13.6

Enter x3 point for a triangle: 14.4

Enter y3 point for a triangle: 17.9

The area of the triangle is 13.114999999999995));