# Find the Diameter or Longest chord of a Circle

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 ` `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

 ` `

Output:

```The length of the longest chord or diameter of the circle is 8
```

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