Given an integer **L**, representing the side length of an **N**-sided regular polygon and integer **K**, the task is to find the side length of the **K ^{th} **

**N**-sided regular polygon formed inside the

**(K – 1)**

^{th}^{ }regular polygon by connecting midpoints of the sides of the

**(K – 1)**polygon.

^{th}**Examples:**

Input:N = 3, L = 6, K = 2Output:3

Input:N = 5, L = 21, K = 7Output:5.88796

**Approach:** The given problem can be solved based on the following observations:

- Suppose, \theta represents the interior angle of the N-sided polygon which is the same for all the polygons formed inside i.e.,
- The length of the side of the first polygon formed inside by connecting midpoints of the sides can be calculated using the formula as .
- The length of the side of the
**K**polygon formed inside the^{th}**(K – 1)**and connecting midpoints of the sides of the^{th}polygon**(K – 1)**is^{th}polygon

Follow the steps below to solve the problem:

- Find the interior angle of the N-sided regular polygon and store it in a variable say
**angle**in radians. - Print the side length after calculating the side length of
**K**N sided regular polygon by the above-discussed formula .^{th}

Below is the implementation of the above approach:

## C++

`// C++ program for the above approach` `#include <bits/stdc++.h>` `using` `namespace` `std;` `#define PI 3.14159265` `// Function to calculate the interior` `// angle of a N-sided regular polygon` `double` `findInteriorAngle(` `int` `n)` `{` ` ` `return` `(n - 2) * PI / n;` `}` `// Function to find the K-th polygon` `// formed inside the (K - 1)th polygon` `double` `calculateSideLength(` `double` `L,` ` ` `int` `N, ` `int` `K)` `{` ` ` `// Stores the interior angle` ` ` `double` `angle = findInteriorAngle(N);` ` ` `// Stores the side length of` ` ` `// K-th regular polygon` ` ` `double` `length = L * ` `pow` `(` `sin` `(angle / 2),` ` ` `(K - 1));` ` ` `// Return the length` ` ` `return` `length;` `}` `// Driver Code` `int` `main()` `{` ` ` `double` `N = 5, L = 21, K = 7;` ` ` `cout << calculateSideLength(L, N, K);` ` ` `return` `0;` `}` |

## Java

`// Java program for the above approach` `import` `java.util.*;` `class` `GFG{` ` ` `static` `final` `double` `PI = ` `3.14159265` `;` `// Function to calculate the interior` `// angle of a N-sided regular polygon` `static` `double` `findInteriorAngle(` `int` `n)` `{` ` ` `return` `((n - ` `2` `) * PI) / n;` `}` `// Function to find the K-th polygon` `// formed inside the (K - 1)th polygon` `static` `double` `calculateSideLength(` `double` `L,` ` ` `int` `N, ` `int` `K)` `{` ` ` ` ` `// Stores the interior angle` ` ` `double` `angle = findInteriorAngle(N);` ` ` `// Stores the side length of` ` ` `// K-th regular polygon` ` ` `double` `length = L * Math.pow(Math.sin(angle / ` `2` `),` ` ` `(K - ` `1` `));` ` ` `// Return the length` ` ` `return` `length;` `}` `// Driver Code` `public` `static` `void` `main(String[] args)` `{` ` ` `double` `L = ` `21` `;` ` ` `int` `N = ` `5` `, K = ` `7` `;` ` ` ` ` `System.out.print(calculateSideLength(L, N, K));` `}` `}` `// This code is contributed by 29AjayKumar` |

## Python3

`# Python3 program for the above approach` `import` `math` `PI ` `=` `3.14159265` `# Function to calculate the interior` `# angle of a N-sided regular polygon` `def` `findInteriorAngle(n):` ` ` `return` `(n ` `-` `2` `) ` `*` `PI ` `/` `n` `# Function to find the K-th polygon` `# formed inside the (K - 1)th polygon` `def` `calculateSideLength(L,` ` ` `N, K):` ` ` `# Stores the interior angle` ` ` `angle ` `=` `findInteriorAngle(N)` ` ` `# Stores the side length of` ` ` `# K-th regular polygon` ` ` `length ` `=` `L ` `*` `pow` `(math.sin(angle ` `/` `2` `),` ` ` `(K ` `-` `1` `))` ` ` `# Return the length` ` ` `return` `length` `# Driver Code` `if` `__name__ ` `=` `=` `"__main__"` `:` ` ` `N ` `=` `5` ` ` `L ` `=` `21` ` ` `K ` `=` `7` ` ` `print` `(calculateSideLength(L, N, K))` ` ` `# This code is contributed by ukasp.` |

## C#

`// C# program for the above approach` `using` `System;` `class` `GFG{` ` ` `static` `readonly` `double` `PI = 3.14159265;` `// Function to calculate the interior` `// angle of a N-sided regular polygon` `static` `double` `findInteriorAngle(` `int` `n)` `{` ` ` `return` `((n - 2) * PI) / n;` `}` `// Function to find the K-th polygon` `// formed inside the (K - 1)th polygon` `static` `double` `calculateSideLength(` `double` `L,` ` ` `int` `N, ` `int` `K)` `{` ` ` ` ` `// Stores the interior angle` ` ` `double` `angle = findInteriorAngle(N);` ` ` `// Stores the side length of` ` ` `// K-th regular polygon` ` ` `double` `length = L * Math.Pow(Math.Sin(angle / 2),` ` ` `(K - 1));` ` ` `// Return the length` ` ` `return` `length;` `}` `// Driver Code` `public` `static` `void` `Main(String[] args)` `{` ` ` `double` `L = 21;` ` ` `int` `N = 5, K = 7;` ` ` ` ` `Console.Write(calculateSideLength(L, N, K));` `}` `}` `// This code is contributed by 29AjayKumar` |

## Javascript

`<script>` ` ` `// Javascript program for the above approach` ` ` `const PI = 3.14159265` ` ` ` ` `// Function to calculate the interior` ` ` `// angle of a N-sided regular polygon` ` ` `function` `findInteriorAngle(n)` ` ` `{` ` ` `return` `(n - 2) * PI / n;` ` ` `}` ` ` `// Function to find the K-th polygon` ` ` `// formed inside the (K - 1)th polygon` ` ` `function` `calculateSideLength(L,` ` ` `N, K) {` ` ` `// Stores the interior angle` ` ` `let angle = findInteriorAngle(N);` ` ` `// Stores the side length of` ` ` `// K-th regular polygon` ` ` `let length = L * Math.pow(Math.sin(angle / 2),` ` ` `(K - 1));` ` ` `// Return the length` ` ` `return` `length;` ` ` `}` ` ` `// Driver Code` ` ` `let N = 5` ` ` `let L = 21` ` ` `let K = 7;` ` ` `document.write(calculateSideLength(L, N, K))` ` ` `</script>` |

**Output:**

5.88796

**Time Complexity:** O(log K)**Auxiliary Space:** O(1)

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