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Area of largest isosceles triangle that can be inscribed in an Ellipse whose vertex coincides with one extremity of the major axis
  • Last Updated : 25 Mar, 2021

Given an ellipse with half the major and minor axes length A & B, the task is to find the area of the largest isosceles triangle that can be inscribed in the ellipse whose vertex coincides with one extremity of the major axis.

Examples:

Input: A = 1, B = 2
Output: 2.598
Explanation:
Area of the isosceles triangle = ((3 * √3) * A * B) / 4.
Therefore, area = 2.598.

Input: A = 2, B = 3
Output: 7.794

 

Approach: The idea is based on the following mathematical formula:



Proof: 

Considering triangle APB, 
Area of APB = AB * PQ = (1 / 2) * A * B * (2 sin∅ – sin2∅)

Taking derivative: 
d(area(APB))/d∅ = ab ( cos∅ – cos2∅)

Equating the derivative to zero: 
d(area(APB))/d∅ = 0 
cos∅ = – (1 / 2) 
∅ = 2PI / 3

Therefore, area of APB = (3√3) * A * B / 4

Below is the implementation of the above approach:

C++




// C++ program for the above approach
 
#include <bits/stdc++.h>
using namespace std;
 
// Function to calculate area
// of the isosceles triangle
void triangleArea(float a, float b)
{
    // If a and b are negative
    if (a < 0 || b < 0) {
        cout << -1;
        return;
    }
 
    // Stores the area of the triangle
    float area = (3 * sqrt(3) * a * b) / (4);
 
    // Print the area
    cout << area;
}
 
// Driver code
int main()
{
    // Given value of a & b
    float a = 1, b = 2;
 
    // Function call to find the
    // area of the isosceles traingle
    triangleArea(a, b);
 
    return 0;
}

Java




// Java program for the above approach
import java.util.*;
 
class GFG
{
 
// Function to calculate area
// of the isosceles triangle
static void triangleArea(float a, float b)
{
   
    // If a and b are negative
    if (a < 0 || b < 0) {
        System.out.println(-1);
        return;
    }
 
    // Stores the area of the triangle
    float area = (3 * (float)Math.sqrt(3) * a * b) / (4);
 
    // Print the area
    System.out.println(area);
}
 
// Driver Code
public static void main(String[] args)
{
   
    // Given value of a & b
    float a = 1, b = 2;
 
    // Function call to find the
    // area of the isosceles traingle
    triangleArea(a, b);
}
}
 
// This code is contributed by sanjoy_62.

Python3




# Python 3 program for the above approach
from math import sqrt
 
# Function to calculate area
# of the isosceles triangle
def triangleArea(a, b):
   
    # If a and b are negative
    if (a < 0 or b < 0):
        print(-1)
        return
 
    # Stores the area of the triangle
    area = (3 * sqrt(3) * a * b) / (4);
 
    # Print the area
    print("{:.5f}".format(area))
 
# Driver code
if __name__ == '__main__':
   
    # Given value of a & b
    a = 1
    b = 2
     
    # Function call to find the
    # area of the isosceles traingle
    triangleArea(a, b)
     
    # This code is contributed by SURENDRA_GANGWAR.

C#




// C# program for the above approach
 
using System;
public class GFG
{
 
  // Function to calculate area
  // of the isosceles triangle
  static void triangleArea(float a, float b)
  {
 
    // If a and b are negative
    if (a < 0 || b < 0) {
      Console.WriteLine(-1);
      return;
    }
 
    // Stores the area of the triangle
    float area = (3 * (float)Math.Sqrt(3) * a * b) / (4);
 
    // Print the area
    Console.WriteLine(area);
  }
 
  // Driver Code
  public static void Main(string[] args)
  {
 
    // Given value of a & b
    float a = 1, b = 2;
 
    // Function call to find the
    // area of the isosceles traingle
    triangleArea(a, b);
  }
}
 
// This code is contributed by AnkThon

Javascript




<script>
 
// Javascript program for the above approach
 
// Function to calculate area
// of the isosceles triangle
function triangleArea(a, b)
{
     
    // If a and b are negative
    if (a < 0 || b < 0)
    {
        document.write(-1);
        return;
    }
 
    // Stores the area of the triangle
    var area = (3 *  Math.sqrt(3) * a * b) / (4);
 
    // Print the area
    document.write(area.toFixed(5));
}
 
// Driver Code
 
// Given value of a & b
var a = 1, b = 2;
 
// Function call to find the
// area of the isosceles traingle
triangleArea(a, b);
 
// This code is contributed by todaysgaurav
 
</script>
Output: 
2.59808

 

Time Complexity: O(1)
Auxiliary Space: O(1)

 

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