# Program to calculate area of inner circle which passes through center of outer circle and touches its circumference

Given a circle **C1 **and it’s a radius **r1**. And one another circle **C2** whose passes through center of circle **C1** and touch the circumference of circle **C1**. The task is to find out the area of circle **C2**. **Examples:**

Input:r1 = 4Output:Area of circle c2 = 12.56Input:r1 = 7Output:Area of circle c2 = 38.465

**Approach: **

Radius **r2** of circle **C2** is .

So we know that the area of circle is .

Below is the implementation of the above approach:

## C++

`// C++ implementation of the above approach` `#include<bits/stdc++.h>` `#include <iostream>` `using` `namespace` `std;` `// Function calculate the area of the inner circle` `double` `innerCirclearea(` `double` `radius)` `{` ` ` `// the radius cannot be negative` ` ` `if` `(radius < 0)` ` ` `{` ` ` `return` `-1;` ` ` `}` ` ` `// area of the circle` ` ` `double` `r = radius / 2;` ` ` `double` `Area = (3.14 * ` `pow` `(r, 2));` ` ` `return` `Area;` `}` `// Driver Code` `int` `main()` `{` ` ` ` ` `double` `radius = 4;` ` ` `cout << (` `"Area of circle c2 = "` `,` ` ` `innerCirclearea(radius));` ` ` `return` `0;` `}` `// This code is contributed by jit_t.` |

## Java

`// Java implementation of the above approach` `class` `GFG {` ` ` `// Function calculate the area of the inner circle` ` ` `static` `double` `innerCirclearea(` `double` `radius)` ` ` `{` ` ` `// the radius cannot be negative` ` ` `if` `(radius < ` `0` `) {` ` ` `return` `-` `1` `;` ` ` `}` ` ` `// area of the circle` ` ` `double` `r = radius / ` `2` `;` ` ` `double` `Area = (` `3.14` `* Math.pow(r, ` `2` `));` ` ` `return` `Area;` ` ` `}` ` ` `// Driver Code` ` ` `public` `static` `void` `main(String arr[])` ` ` `{` ` ` `double` `radius = ` `4` `;` ` ` `System.out.println(` `"Area of circle c2 = "` ` ` `+ innerCirclearea(radius));` ` ` `}` `}` |

## Python3

`# Python3 implementation of the above approach` `# Function calculate the area of the inner circle` `def` `innerCirclearea(radius) :` ` ` `# the radius cannot be negative` ` ` `if` `(radius < ` `0` `) :` ` ` `return` `-` `1` `;` ` ` ` ` `# area of the circle` ` ` `r ` `=` `radius ` `/` `2` `;` ` ` `Area ` `=` `(` `3.14` `*` `pow` `(r, ` `2` `));` ` ` `return` `Area;` ` ` `# Driver Code` `if` `__name__ ` `=` `=` `"__main__"` `:` ` ` ` ` `radius ` `=` `4` `;` ` ` `print` `(` `"Area of circle c2 ="` `,` ` ` `innerCirclearea(radius));` `# This code is contributed by AnkitRai01` |

## C#

`// C# Implementation of the above approach` `using` `System;` ` ` `class` `GFG` `{` ` ` `// Function calculate the area` ` ` `// of the inner circle` ` ` `static` `double` `innerCirclearea(` `double` `radius)` ` ` `{` ` ` `// the radius cannot be negative` ` ` `if` `(radius < 0)` ` ` `{` ` ` `return` `-1;` ` ` `}` ` ` `// area of the circle` ` ` `double` `r = radius / 2;` ` ` `double` `Area = (3.14 * Math.Pow(r, 2));` ` ` `return` `Area;` ` ` `}` ` ` `// Driver Code` ` ` `public` `static` `void` `Main(String []arr)` ` ` `{` ` ` `double` `radius = 4;` ` ` `Console.WriteLine(` `"Area of circle c2 = "` `+` ` ` `innerCirclearea(radius));` ` ` `}` `}` `// This code is contributed by PrinciRaj1992` |

## Javascript

`<script>` `// JavaScript implementation of the above approach` `// Function calculate the area of the inner circle` `function` `innerCirclearea(radius)` `{` ` ` `// the radius cannot be negative` ` ` `if` `(radius < 0)` ` ` `{` ` ` `return` `-1;` ` ` `}` ` ` `// area of the circle` ` ` `let r = radius / 2;` ` ` `let Area = (3.14 * Math.pow(r, 2));` ` ` `return` `Area;` `}` `// Driver Code` ` ` ` ` `let radius = 4;` ` ` `document.write(` `"Area of circle c2 = "` `+` ` ` `innerCirclearea(radius));` `// This code is contributed by Surbhi Tyagi.` `</script>` |

**Output:**

Area of circle c2 = 12.56

**Time Complexity :** O(log r) ,where r is the radius of circle.

**Auxiliary Space :** O(1) ,as we are not using any extra space.