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

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  • Last Updated : 23 Jun, 2022
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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)n
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)


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