Chapter 2 Exercise 19, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

*2.19 (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:

import java.util.Scanner;
 
public class ProgrammingEx2_19 {
 
 public static void main(String[] args) {
  Scanner input = new Scanner(System.in);
 
  System.out.print("Enter three points for a triangle:");
  double x1 = input.nextDouble();
  double y1 = input.nextDouble();
  double x2 = input.nextDouble();
  double y2 = input.nextDouble();
  double x3 = input.nextDouble();
  double y3 = input.nextDouble();
 
  double side1 = Math.sqrt(Math.pow(x1 - x2, 2) + Math.pow(y1 - y2, 2));
  double side2 = Math.sqrt(Math.pow(x2 - x3, 2) + Math.pow(y2 - y3, 2));
  double side3 = Math.sqrt(Math.pow(x1 - x3, 2) + Math.pow(y1 - y3, 2));
  double s = (side1 + side2 + side3) / 2;
  double area = Math.sqrt(s * (s - side1) * (s - side2) * (s - side3));
 
  System.out.print("The area of the triangle is  " + area);
 
 }
}