Given a semicircle with radius **r**, we have to find the largest square that can be inscribed in the semicircle, with base lying on the diameter.**Examples:**

Input: r = 5 Output: 20 Input: r = 8 Output: 51.2

**Approach**: Let **r** be the radius of the semicircle & a be the side length of the **square**.

From the figure we can see that, centre of the circle is also the midpoint of the base of the square.So in the right angled triangle **AOB**, from **Pythagorus Theorem**:

a^2 + (a/2)^2 = r^2

5*(a^2/4) = r^2

a^2 = 4*(r^2/5) i.e. area of the square

**Below is the implementation of the above approach**:

## C++

`// C++ Program to find the biggest square` `// which can be inscribed within the semicircle` `#include <bits/stdc++.h>` `using` `namespace` `std;` `// Function to find the area` `// of the squaare` `float` `squarearea(` `float` `r)` `{` ` ` `// the radius cannot be negative` ` ` `if` `(r < 0)` ` ` `return` `-1;` ` ` `// area of the square` ` ` `float` `a = 4 * (` `pow` `(r, 2) / 5);` ` ` `return` `a;` `}` `// Driver code` `int` `main()` `{` ` ` `float` `r = 5;` ` ` `cout << squarearea(r) << endl;` ` ` `return` `0;` `}` |

## Java

`// Java Program to find the biggest square` `// which can be inscribed within the semicircle` `import` `java.io.*;` `class` `GFG {` `// Function to find the area` `// of the squaare` `static` `float` `squarearea(` `float` `r)` `{` ` ` `// the radius cannot be negative` ` ` `if` `(r < ` `0` `)` ` ` `return` `-` `1` `;` ` ` `// area of the square` ` ` `float` `a = ` `4` `* (` `float` `)(Math.pow(r, ` `2` `) / ` `5` `);` ` ` `return` `a;` `}` `// Driver code` ` ` `public` `static` `void` `main (String[] args) {` ` ` `float` `r = ` `5` `;` ` ` `System.out.println( squarearea(r));` ` ` `}` `}` `// This code is contributed by chandan_jnu.` |

## Python3

`# Python 3 program to find the` `# biggest square which can be` `# inscribed within the semicircle` `# Function to find the area` `# of the squaare` `def` `squarearea(r):` ` ` `# the radius cannot be` ` ` `# negative` ` ` `if` `(r < ` `0` `):` ` ` `return` `-` `1` ` ` `# area of the square` ` ` `a ` `=` `4` `*` `(` `pow` `(r, ` `2` `) ` `/` `5` `)` ` ` `return` `a` `# Driver code` `if` `__name__ ` `=` `=` `"__main__"` `:` ` ` ` ` `r ` `=` `5` ` ` `print` `(` `int` `(squarearea(r)))` `# This code is contributed` `# by ChitraNayal` |

## C#

`// C# Program to find the` `// biggest square which can be` `// inscribed within the semicircle` `using` `System;` `class` `GFG` `{` `// Function to find the` `// area of the squaare` `static` `float` `squarearea(` `float` `r)` `{` ` ` `// the radius cannot be negative` ` ` `if` `(r < 0)` ` ` `return` `-1;` ` ` `// area of the square` ` ` `float` `a = 4 * (` `float` `)(Math.Pow(r, 2) / 5);` ` ` `return` `a;` `}` `// Driver code` `public` `static` `void` `Main ()` `{` ` ` `float` `r = 5;` ` ` `Console.WriteLine(squarearea(r));` `}` `}` `// This code is contributed` `// by anuj_67` |

## PHP

`<?php` `// PHP Program to find the` `// biggest square which can be` `// inscribed within the semicircle` `// Function to find the area` `// of the squaare` `function` `squarearea(` `$r` `)` `{` ` ` `// the radius cannot be negative` ` ` `if` `(` `$r` `< 0)` ` ` `return` `-1;` ` ` `// area of the square` ` ` `$a` `= 4 * (pow(` `$r` `, 2) / 5);` ` ` `return` `$a` `;` `}` `// Driver code` `$r` `= 5;` `echo` `squarearea(` `$r` `);` `// This code is contributed` `// by Shivi_Aggarwal` `?>` |

## Javascript

`<script>` `// javascript Program to find the biggest square` `// which can be inscribed within the semicircle` `// Function to find the area` `// of the squaare` `function` `squarearea(r)` `{` ` ` `// the radius cannot be negative` ` ` `if` `(r < 0)` ` ` `return` `-1;` ` ` `// area of the square` ` ` `var` `a = 4 * (Math.pow(r, 2) / 5);` ` ` `return` `a;` `}` `// Driver code` `var` `r = 5;` `document.write( squarearea(r));` `// This code contributed by Princi Singh` `</script>` |

**Output:**

20

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