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# Sum of series 2/3 – 4/5 + 6/7 – 8/9 + ——- upto n terms

• Last Updated : 18 Mar, 2021

Given the value of n, find the sum of the series (2 / 3) – (4 / 5) + (6 / 7) – (8 / 9) + – – – – – – – upto n terms.
Examples :

```Input : n = 5
Output : 0.744012
Series : (2 / 3) - (4 / 5) + (6 / 7) - (8 / 9) + (10 / 11)

Input : n = 7
Output : 0.754268
Series : (2 / 3) - (4 / 5) + (6 / 7) - (8 / 9) +
(10 / 11) - (12 / 13) + (14 / 15)```

## C++

 `// C++ program to find``// sum of given series``#include ``using` `namespace` `std;` `// Function to find sum of series``// up-to n terms``double` `seriesSum(``int` `n)``{``    ``// initializing counter by 1``    ``int` `i = 1;``    ` `    ``// variable to calculate result``    ``double` `res = 0.0;``    ``bool` `sign = ``true``;``    ` `    ``// while loop until nth term``    ``// is not reached``    ``while` `(n > 0)``    ``{``        ``n--;``        ` `        ``// boolean type variable``        ``// for checking validation``        ``if` `(sign) {``            ``sign = !sign;``            ``res = res + (``double``)++i / ++i;``        ``}``        ``else` `{``            ``sign = !sign;``            ``res = res - (``double``)++i / ++i;``        ``}``    ``}``    ` `    ``return` `res;``}` `// Driver Code``int` `main()``{``    ``int` `n = 5;``    ``cout << seriesSum(n);   ``    ``return` `0;``}`

## Java

 `// Java program to find``// sum of given series``import` `java.io.*;` `class` `GFG {``    ` `    ``// Function to find sum of series``    ``// up-to n terms``    ``static` `double` `seriesSum(``int` `n)``    ``{``    ` `    ``// initializing counter by 1``    ``int` `i = ``1``;``    ` `    ``// variable to calculate result``    ``double` `res = ``0.0``;``    ``boolean` `sign = ``true``;``    ` `    ``// while loop until nth term``    ``// is not reached``    ``while` `(n > ``0``)``    ``{``        ``n--;``        ` `        ``// boolean type variable``        ``// for checking validation``        ``if` `(sign)``        ``{``            ``sign = !sign;``            ``res = res + (``double``)++i / ++i;``        ``}``        ` `        ``else``        ``{``            ``sign = !sign;``            ``res = res - (``double``)++i / ++i;``        ``}``    ``}``    ` `    ``return` `res;``}``    ` `    ``// Driver Code``    ``public` `static` `void` `main (String[] args) {``        ` `        ``int` `n = ``5``;``        ` `        ``System.out.print(seriesSum(n));``    ``}``}` `// This code is contributed by vt_m`

## Python3

 `# Python3 program to find``# sum of given series` `# Function to find``# sum of series``# up-to n terms``def` `seriesSum(n):``    ` `    ``# initializing``    ``# counter by 1``    ``i ``=` `1``;``    ` `    ``# variable to``    ``# calculate result``    ``res ``=` `0.0``;``    ``sign ``=` `True``;``    ` `    ``# while loop until nth``    ``# term is not reached``    ``while` `(n > ``0``):``        ``n ``=` `n ``-` `1``;``        ` `        ``# boolean type variable``        ``# for checking validation``        ``if` `(sign):``            ``sign ``=` `False``;``            ``res ``=` `res ``+` `(i ``+` `1``) ``/` `(i ``+` `2``);``            ``i ``=` `i ``+` `2``;``        ``else``:``            ``sign ``=` `True``;``            ``res ``=` `res ``-` `(i ``+` `1``) ``/` `(i ``+` `2``);``            ``i ``=` `i ``+` `2``;``    ` `    ``return` `res;` `# Driver Code``n ``=` `5``;``print``(``round``(seriesSum(n), ``6``));` `# This code is contributed``# by mits`

## C#

 `// C# program to find``// sum of given series``using` `System;` `class` `GFG {``    ` `    ``// Function to find sum of``    ``// series up-to n terms``    ``static` `double` `seriesSum(``int` `n)``    ``{``    ` `    ``// initializing counter by 1``    ``int` `i = 1;``    ` `    ``// variable to calculate result``    ``double` `res = 0.0;``    ``bool` `sign = ``true``;``    ` `    ``// while loop until nth term``    ``// is not reached``    ``while` `(n > 0)``    ``{``        ``n--;``        ` `        ``// boolean type variable``        ``// for checking validation``        ``if` `(sign)``        ``{``            ``sign = !sign;``            ``res = res + (``double``)++i / ++i;``        ``}``        ` `        ``else``        ``{``            ``sign = !sign;``            ``res = res - (``double``)++i / ++i;``        ``}``    ``}``    ` `    ``return` `res;``}``    ` `    ``// Driver Code``    ``public` `static` `void` `Main () {``        ` `        ``int` `n = 5;``        ``Console.Write(seriesSum(n));``    ``}``}` `// This code is contributed by vt_m`

## PHP

 ` 0)``    ``{``        ``\$n``--;``        ` `        ``// boolean type variable``        ``// for checking validation``        ``if` `(``\$sign``) {``            ``\$sign` `= !``\$sign``;``            ``\$res` `= ``\$res` `+ (double)++``\$i` `/ ++``\$i``;``        ``}``        ``else` `{``            ``\$sign` `= !``\$sign``;``            ``\$res` `= ``\$res` `- (double)++``\$i` `/ ++``\$i``;``        ``}``    ``}``    ` `    ``return` `\$res``;``}` `// Driver Code``\$n` `= 5;``echo``(seriesSum(``\$n``));` `// This code is contributed by Ajit.``?>`

## Javascript

 ``

Output :

`0.744012`

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