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

Input:a = 6Output:10.38Input:a = 9Output:15.57

**Approach:** We know that the sum of interior angles of a polygon = **(n – 2) * 180** where, **n** is the number of sides of the polygon.

So, sum of interior angles of a hexagon = **4 * 180 = 720** and each interior angle will be **120**.

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(60) = x / a** i.e. **x = 0.866 * a**

Therefore, diagonal length will be **2 * x** i.e. **1.73 * a**.

Below is the implementation of the above approach:

## C++

`// C++ Program to find the diagonal` `// of a regular hexagon` `#include <bits/stdc++.h>` `using` `namespace` `std;` `// Function to find the diagonal` `// of a regular hexagon` `float` `hexDiagonal(` `float` `a)` `{` ` ` `// Side cannot be negative` ` ` `if` `(a < 0)` ` ` `return` `-1;` ` ` `// Length of the diagonal` ` ` `float` `d = 1.73 * a;` ` ` `return` `d;` `}` `// Driver code` `int` `main()` `{` ` ` `float` `a = 9;` ` ` `cout << hexDiagonal(a) << endl;` ` ` `return` `0;` `}` |

## Java

`// Java Program to find the diagonal` `// of a regular hexagon` `public` `class` `GFG` `{` ` ` `// Function to find the diagonal` ` ` `// of a regular hexagon` ` ` `static` `double` `hexDiagonal(` `float` `a)` ` ` `{` ` ` ` ` `// Side cannot be negative` ` ` `if` `(a < ` `0` `)` ` ` `return` `-` `1` `;` ` ` ` ` `// Length of the diagonal` ` ` `double` `d = (` `double` `)` `1.73` `* a;` ` ` `return` `d;` ` ` `}` ` ` ` ` `// Driver code` ` ` `public` `static` `void` `main(String []args)` ` ` `{` ` ` `float` `a = ` `9` `;` ` ` `System.out.println(hexDiagonal(a)) ;` ` ` `}` ` ` `// This code is contributed by Ryuga` `}` |

## Python3

`# Python3 Program to find the diagonal` `# of a regular hexagon` `# Function to find the diagonal` `# of a regular hexagon` `def` `hexDiagonal(a):` ` ` `# Side cannot be negative` ` ` `if` `(a < ` `0` `):` ` ` `return` `-` `1` `;` ` ` `# Length of the diagonal` ` ` `d ` `=` `1.73` `*` `a;` ` ` `return` `d;` `# Driver code` `a ` `=` `9` `;` `print` `(hexDiagonal(a));` `# This code is contributed` `# by Akanksha Rai` |

## C#

`// C# Program to find the diagonal ` `// of a regular hexagon` `using` `System ;` `public` `class` `GFG` `{` ` ` ` ` `// Function to find the diagonal ` ` ` `// of a regular hexagon ` ` ` `static` `double` `hexDiagonal(` `float` `a) ` ` ` `{ ` ` ` ` ` `// Side cannot be negative ` ` ` `if` `(a < 0) ` ` ` `return` `-1; ` ` ` ` ` `// Length of the diagonal ` ` ` `double` `d = (` `double` `)1.73 * a; ` ` ` `return` `d; ` ` ` `} ` ` ` ` ` `// Driver code ` ` ` `public` `static` `void` `Main()` ` ` `{ ` ` ` `float` `a = 9; ` ` ` `Console.WriteLine(hexDiagonal(a)) ; ` ` ` `} ` ` ` `// This code is contributed by Subhadeep` `}` |

## PHP

`<?php` `// PHP Program to find the diagonal` `// of a regular hexagon` `// Function to find the diagonal` `// of a regular hexagon` `function` `hexDiagonal(` `$a` `)` `{` ` ` `// Side cannot be negative` ` ` `if` `(` `$a` `< 0)` ` ` `return` `-1;` ` ` `// Length of the diagonal` ` ` `$d` `= 1.73 * ` `$a` `;` ` ` `return` `$d` `;` `}` `// Driver code` `$a` `= 9;` `echo` `hexDiagonal(` `$a` `), ` `"\n"` `;` `// This code is contributed` `// by akt_mit` `?>` |

## Javascript

`<script>` `// javascript Program to find the diagonal` `// of a regular hexagon` `// Function to find the diagonal` `// of a regular hexagon` `function` `hexDiagonal(a)` `{` ` ` `// Side cannot be negative` ` ` `if` `(a < 0)` ` ` `return` `-1;` ` ` `// Length of the diagonal` ` ` `var` `d = 1.73 * a;` ` ` `return` `d;` `}` ` ` ` ` `// Driver code` `var` `a = 9;` `document.write(hexDiagonal(a)) ;` `// This code contributed by Princi Singh` `</script>` |

**Output:**

15.57

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