Program to find the nth term of the series -2, 4, -6, 8….

Given a number N, the task is to find the Nth term of the following series. 

-2, 4, -6, 8…… 

Examples:

Input: n=4
Output: 8

Input: n=3
Output: -6

Approach: By clearly examining the series we can find the Tn term for the series and with the help of tn we can find the desired result.

Tn=-2 + 4 -6 +8 ….. 
We can see that here odd terms are negative and even terms are positive 
Tn=2(-1)ⁿn 
Tn=(-1)ⁿ2n 

Below is the implementation of above approach.

CPP

// C++ implementation of the approach

#include <bits/stdc++.h>
using namespace std;

// Function to return the
// nth term of the given series
long Nthterm(int n)
{

    // nth term
    int Tn = pow(-1, n) * 2 * n;

    return Tn;
}

// Driver code
int main()
{
    int n = 3;

    cout << Nthterm(n);

    return 0;
}

Python

# Python3 implementation of the approach

# Function to return the nth term of the given series
def Nthterm(n):

    # nth term
    Tn = ((-1)**n) * (2 * n)

    return Tn;


# Driver code
n = 3
print(Nthterm(n))

Java

// Java implementation of the approach
import java.util.*;
import java.lang.*;
import java.io.*;

public class GFG {

    // Function to return the nth term of the given series
    static int NthTerm(int n)
    {
        int Tn
            = ((int)Math.pow(-1, n)) * 2 * n;

        return Tn;
    }

    // Driver code
    public static void main(String[] args)
    {
        int n = 3;
        System.out.println(NthTerm(n));
    }
}

C#

// C# implementation of the approach
using System;
public class GFG {

    // Function to return the nth term of the given series
    static int NthTerm(int n)
    {

        int Tn
            = ((int)Math.Pow(-1, n) * 2 * n);

        return Tn;
    }

    // Driver code
    public static void Main()
    {
        int n = 3;
        Console.WriteLine(NthTerm(n));
    }
}

PHP

<?php
// PHP implementation of the approach

// Function to return the nth term of the given series
function Nthterm($n)
{

    $Tn = (pow(-1, $n)) * (2*n);

    // nth term of the given series
    return $Tn;

}

// Driver code
$n = 3;
echo Nthterm($n);
?>

Javascript

<script>

// JavaScript implementation of the approach

// Function to return the
// nth term of the given series
function Nthterm( n)
{

    // nth term
    let Tn = Math.pow(-1, n) * 2 * n;

    return Tn;
}


// Driver Function

    // get the value of N
    let N = 3;

    // Calculate and print the Nth term
    document.write( Nthterm(N));

// This code is contributed by todaysgaurav

</script>

Output:

-6

Time Complexity: O(log n)

Auxiliary Space: O(1)