Iterative Constructs in Java

Chapter 9

Iterative Constructs in Java

Class 10 - Logix Kips ICSE Computer Applications with BlueJ

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Java Program: Sum of Alternating Powers Series

30(ii). Write a program in Java to find the sum of the given series:

x¹ - x² + x³ - x⁴ + ..... - xⁿ , where x = 3

Program Title: Sum of Alternating Powers Series

Here’s a Java program to compute the alternating series:

x¹ − x² + x³ − x⁴ + ⋯ ± xⁿ

with x = 3.

public class AlternatingSeries {
    public static void main(String[] args) {
        int x = 3; // value of x
        int n = 5; // number of terms, can be changed
        int sign = 1; // to alternate + and -
        double sum = 0.0;
 
        for (int i = 1; i <= n; i++) {
            sum += sign * Math.pow(x, i);
            sign *= -1; // alternate the sign
        }
 
        System.out.println("Sum of the series for x = " + x + " and n = " + n + " is: " + sum);
    }
}
 

Sample Input / Output (n = 5)
Sum of the series for x = 3 and n = 5 is: 177.0

📝 Explanation

3¹ – 3² + 3³ – 3⁴ + 3⁵ = 3 – 9 + 27 – 81 + 243 = 177

How It Works

1. sign variable starts at +1
2. For each term, multiply the power of x with sign
3. Flip the sign using sign *= -1 to alternate between + and -
4. Sum all terms to get the result