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

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. ` `?> `

Output :

```0.744012
```

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Improved By : jit_t, Mithun Kumar