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Diagonal of a Regular Heptagon
• Last Updated : 17 Mar, 2021

Given an integer a which is the side of a regular heptagon, the task is to find and print the length of its diagonal. Examples:

Input: a = 6
Output: 10.812
Input: a = 9
Output: 16.218

Approach: We know that the sum of interior angles of a polygon = (n – 2) * 180 where, n is the no. of sides in the polygon.
So, sum of interior angles of heptagon = 5 * 180 = 900 and each interior angle will be 128.58(Approx).
Now, we have to find BC = 2 * x. If we draw a perpendicular AO on BC, we will see that the perpendicular bisects BC in BO and OC, as triangles AOB and AOC are congruent to each other.
So, in triangle AOB, sin(64.29) = x / a i.e. x = 0.901 * a
Therefore, diagonal length will be 2 * x i.e. 1.802 * a.
Below is the implementation of the above approach:

## C++

 `// C++ Program to find the diagonal``// of a regular heptagon``#include ``using` `namespace` `std;` `// Function to return the diagonal``// of a regular heptagon``float` `heptdiagonal(``float` `a)``{` `    ``// Side cannot be negative``    ``if` `(a < 0)``        ``return` `-1;` `    ``// Length of the diagonal``    ``float` `d = 1.802 * a;``    ``return` `d;``}` `// Driver code``int` `main()``{``    ``float` `a = 6;``    ``cout << heptdiagonal(a) << endl;``    ``return` `0;``}`

## Java

 `// Java program to find the diagonal of a regular heptagon``import` `java.util.*;``import` `java.lang.*;``import` `java.io.*;` `public` `class` `GFG {` `    ``// Function to return the diagonal of a regular heptagon``    ``static` `double` `heptdiagonal(``double` `a)``    ``{` `//side cannot be negative``        ``if``(a<``0``)``        ``return` `-``1``;` `        ``// length of the diagonal``        ``double` `d=``1.802``*a;``        ` `        ``return` `d;``    ``}` `    ``// Driver code``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `a = ``6``;``        ``System.out.println(heptdiagonal(a));``    ``}``}`

## Python3

 `# Python3 Program to find the diagonal``# of a regular heptagon` `# Function to return the diagonal``# of a regular heptagon``def` `heptdiagonal(a) :` `    ``# Side cannot be negative``    ``if` `(a < ``0``) :``        ``return` `-``1` `    ``# Length of the diagonal``    ``d ``=` `1.802` `*` `a``    ` `    ``return` `round``(d, ``3``)` `# Driver code``if` `__name__ ``=``=` `"__main__"` `:` `    ``a ``=` `6``    ``print``(heptdiagonal(a))` `# This code is contributed by Ryuga`

## C#

 `// C# program to find the diagonal of a regular heptagon``using` `System;``public` `class` `GFG {` `    ``// Function to return the diagonal of a regular heptagon``    ``static` `double` `heptdiagonal(``double` `a)``    ``{` `//side cannot be negative``        ``if``(a<0)``        ``return` `-1;` `        ``// length of the diagonal``        ``double` `d=1.802*a;``        ` `        ``return` `d;``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main()``    ``{``        ``int` `a = 6;``        ``Console.WriteLine(heptdiagonal(a));``    ``}``} ``// This code is contributed by Mukul singh`

## PHP

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## Javascript

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Output:
`10.812`

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