程序找到系列-2、4，-6、8…的第n个项。

给定数字N ，任务是找到以下系列的第N个项。

-2, 4, -6, 8…… 
 

例子：

Input: n=4
Output: 8

Input: n=3
Output: -6

方法：通过清楚地检查序列，我们可以找到该序列的Tn项，并且在tn的帮助下，我们可以找到所需的结果。

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 
 

下面是上述方法的实现。

CPP

// C++ implementation of the approach
 
#include 
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));
    }
}

Javascript

 
// 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
 

输出：

-6