What is the area of the largest rectangle that can be inscribed in a semicircle of radius 10

#include <bits/stdc++.h>

using namespace std;

float rectanglearea(float r)

{

    if (r < 0)

        return -1;

    float a = r * r;

    return a;

}

int main()

{

    float r = 5;

    cout << rectanglearea(r) << endl;

    return 0;

}

class GFG

{

static float rectanglearea(float r)

{

if (r < 0)

    return -1;

float a = r * r;

return a;

}

public static void main(String[] args)

{

    float r = 5;

    System.out.println((int)rectanglearea(r));

}

}

def rectanglearea(r) :

    if r < 0 :

        return -1

    a = r * r

    return a

if __name__ == "__main__" :

    r = 5

    print(rectanglearea(r))

using System;

class GFG

{

static float rectanglearea(float r)

{

if (r < 0)

    return -1;

float a = r * r;

return a;

}

public static void Main()

{

    float r = 5;

    Console.Write((int)rectanglearea(r));

}

}

<?php

function rectanglearea($r)

{

    if ($r < 0)

        return -1;

    $a = $r * $r;

    return $a;

}

$r = 5;

echo rectanglearea($r)."\n";

?>

<script>

function rectanglearea(r)

{

    if (r < 0)

        return -1;

    var a = r * r;

    return a;

}

var r = 5;

document.write(parseInt(rectanglearea(r)));

</script>