Chapter 4 Exercise 5, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

*4.5 (Geometry: area of a regular polygon) A regular polygon is an n-sided polygon in which all sides are of the same length and all angles have the same degree (i.e., the polygon is both equilateral and equiangular). The formula for computing the area of a regular polygon is$$Area=\frac{n\ast s^2}{4\tan (\frac{\pi }{n}})$$Here, s is the length of a side. Write a program that prompts the user to enter the number of sides and their length of a regular polygon and displays its area. Here is a sample run:

Enter the number of sides: 5
Enter the side: 6.5
The area of the polygon is 74.69017017488385 

import java.util.Scanner;
 
 
public class ProgrammingEx4_5 {
 
 public static void main(String[] args) {
  Scanner input = new Scanner(System.in);
  System.out.print("Enter the number of sides:");
  double n = input.nextDouble();
   
  System.out.print("Enter the side:");
  double s = input.nextDouble();
   
  double area = n * Math.pow(s, 2) / (4 * Math.tan(Math.PI / n));
 
  System.out.println("The area of the polygon is " + area);
 
 }
 
}