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Largest square that can be inscribed in a semicircle

  • Last Updated : 09 Sep, 2021

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 Pythagoras 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 square
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 square
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 square
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 square
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 square
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 square
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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