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Find the Diameter or Longest chord of a Circle
  • Last Updated : 19 Mar, 2021

Given a circle with radius ‘r’ is given, the task is to find the diameter or longest chord of the circle.
Examples: 
 

Input: r = 4
Output: 8

Input: r = 9
Output: 18

 

Proof that the Longest chord of a circle is its Diameter: 
 

  • Draw circle O and any chord AB on it.
  • From one endpoint of the chord, say A, draw a line segment through the centre. That is, draw a diameter.
  • Now draw a radius from centre O to B.
  • By the triangle inequality, 
     
AB < AO + OB
 = r + r
 = 2r
 = d
  • So, any chord that is not a diameter will be smaller than a diameter.
  • So the largest chord is a diameter

Approach:
 



  • The Longest chord of any circle is its diameter.
  • Therefore, the diameter of a circle is twice the radius of it.
     
Length of the longest chord or diameter = 2r
  •  

Below is the implementation of the above approach: 
 

C++




// C++ program to find
// the longest chord or diameter
// of the circle whose radius is given
 
#include <bits/stdc++.h>
using namespace std;
 
// Function to find the longest chord
void diameter(double r)
{
    cout << "The length of the longest chord"
         << " or diameter of the circle is "
         << 2 * r << endl;
}
 
// Driver code
int main()
{
 
    // Get the radius
    double r = 4;
 
    // Find the diameter
    diameter(r);
 
    return 0;
}

Java




// Java program to find
// the longest chord or diameter
// of the circle whose radius is given
class GFG
{
     
// Function to find the longest chord
static void diameter(double r)
{
    System.out.println("The length of the longest chord"
        + " or diameter of the circle is "
        + 2 * r);
}
 
// Driver code
public static void main(String[] args)
{
     
    // Get the radius
    double r = 4;
 
    // Find the diameter
    diameter(r);
}
}
 
// This code contributed by Rajput-Ji

Python3




# Python3 program to find
# the longest chord or diameter
# of the circle whose radius is given
 
# Function to find the longest chord
def diameter(r):
 
    print("The length of the longest chord"
        ," or diameter of the circle is "
        ,2 * r)
 
 
# Driver code
 
# Get the radius
r = 4
 
# Find the diameter
diameter(r)
 
# This code is contributed by mohit kumar

C#




// C# program to find
// the longest chord or diameter
// of the circle whose radius is given
using System;
 
class GFG
{
     
// Function to find the longest chord
static void diameter(double r)
{
    Console.WriteLine("The length of the longest chord"
        + " or diameter of the circle is "
        + 2 * r);
}
 
// Driver code
public static void Main(String[] args)
{
     
    // Get the radius
    double r = 4;
 
    // Find the diameter
    diameter(r);
}
}
 
// This code has been contributed by 29AjayKumar

PHP




<?php
// PHP program to find
// the longest chord or diameter
// of the circle whose radius is given
 
// Function to find the longest chord
function diameter($r)
{
    echo "The length of the longest chord"
        ," or diameter of the circle is "
        ,2 * $r << "\n";
}
 
    // Driver code
    // Get the radius
    $r = 4;
 
    // Find the diameter
    diameter($r);
     
    // This code is contributed by Ryuga
 
?>

Javascript




<script>
 
// javascript program to find
// the longest chord or diameter
// of the circle whose radius is given
  
// Function to find the longest chord
function diameter(r)
{
    document.write("The length of the longest chord"
        + " or diameter of the circle is "
        + 2 * r);
}
 
// Driver code
     
// Get the radius
var r = 4;
 
// Find the diameter
diameter(r);
 
// This code contributed by Princi Singh
 
</script>
Output: 
The length of the longest chord or diameter of the circle is 8

 

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