Java Program to Find Sum of First N Terms of Geometric Progression

In this post we will see a java program to calculate sum of first n terms of a geometric progression. Geometric progression is also called GP (short for Geometric progression). The equation to find sum of first n terms of a geometric progression is as follows:

sum= a*(1-r^n)/(1-r)

sum of first n terms of geometric progression

Now, we will see a java program to find sum of first n terms of a GP. There is a case in which the above equation fails. When r (common ratio) is 1, the above equation won't work. Then every term in the GP will be same as first term. Therefore, in that case, the sum is a*n. The program is as follows:

import java.util.Scanner;

public class SumGP {
public static void main(String[] arg)
    {
    Scanner sc=new Scanner(System.in);
    System.out.println("Enter first term, common ratio and n (number of terms)");
    int a=sc.nextInt(),r=sc.nextInt(),n=sc.nextInt();
        System.out.println((r==1)?"Sum is:"+a*n:"Sum is:"+(float)a*(1-Math.pow(r,n))/(1-r));
    }
}