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Find if two given Quadratic equations have common roots or not
  • Last Updated : 08 Jun, 2020

Given values a1, b1 and c1 of first Quadratic equations a_{1}x^{2} + b_{1}x + c_{1} = 0 and values a2, b2 and c2 of second Quadratic equations a_{2}x^{2} + b_{2}x + c_{2} = 0, the task is to find whether both quadratic equations have common roots or not.

Examples:

Input: a1 = 1, b1 = -5, c1 = 6, a2 = 2, b2 = -10, c2 = 12
Output: Yes
Explanation:
Roots of both quadratic equations are (2, 3)

Input: a1 = 1, b1 = -5, c1 = 6, a2 = 1, b2 = -9, c2 = 20
Output: No
Explanation:
Roots of first quadratic equations are (2, 3), and Roots of second quadratic equations are (4, 5)
Therefore, both quadratic equations have differnt roots.

Approach:
Let the two quadratic equations are a_{1}x^{2} + b_{1}x + c_{1} = 0 and a_{2}x^{2} + b_{2}x + c_{2} = 0



  • Let us assume the given condition to be true, i.e. both the equations have common roots, say \alpha and \beta
  • As we know that
    \text{Sum of roots = } -\frac{b}{a} and \text{Product of roots = } \frac{c}{a}
    where a, b, c represents the quadratic equation ax^{2} + bx + c = 0

  • Therefore,
    For 1st quadratic equation:
    \text{Sum of roots = } \alpha + \beta = -\frac{b_{1}}{a_{1}}
    \text{Product of roots = } \alpha \beta =  \frac{c_{1}}{a_{1}}

    Similarly, for 2nd quadratic equation:
    \text{Sum of roots = } \alpha + \beta = -\frac{b_{2}}{a_{2}}
    \text{Product of roots = } \alpha \beta =  \frac{c_{2}}{a_{2}}

  • Now since both the roots are common,
    Therfore, from above equations
    \alpha + \beta = -\frac{b_{1}}{a_{1}} = -\frac{b_{2}}{a_{2}}
    \Rightarrow   \frac{a_{1}}{a_{2}} = \frac{b_{1}}{b_{2}}

  • Also,
    \alpha \beta = \frac{c_{1}}{a_{1}} = \frac{c_{2}}{a_{2}}
    \Rightarrow  \frac{c_{1}}{c_{2}} = \frac{a_{1}}{a_{2}}

  • Combining the above equations:

    \frac{a_{1}}{a_{2}} = \frac{b_{1}}{b_{2}} = \frac{c_{1}}{c_{2}}

    which is the required condition for both roots to be common of the two quadratic equations.

Programs:

C++

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// C++ Program to Find if two given
// Quadratic equations have
// common roots or not
  
#include <iostream>
using namespace std;
  
// function to check if 2 quadratic
// equations have common roots or not.
bool checkSolution(float a1, float b1,
                   float c1, float a2,
                   float b2, float c2)
{
    return (a1 / a2) == (b1 / b2)
           && (b1 / b2) == (c1 / c2);
}
  
// Driver code
int main()
{
    float a1 = 1, b1 = -5, c1 = 6;
    float a2 = 2, b2 = -10, c2 = 12;
    if (checkSolution(a1, b1, c1, a2, b2, c2))
        cout << "Yes";
    else
        cout << "No";
    return 0;
}

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Java

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// Java Program to Find if two given
// quadratic equations have common 
// roots or not
class GFG {
      
// Function to check if 2 quadratic
// equations have common roots or not.
static boolean checkSolution(float a1, float b1,
                             float c1, float a2,
                             float b2, float c2)
{
    return ((a1 / a2) == (b1 / b2) && 
            (b1 / b2) == (c1 / c2));
}
      
// Driver code
public static void main (String[] args) 
{
    float a1 = 1, b1 = -5, c1 = 6;
    float a2 = 2, b2 = -10, c2 = 12;
          
    if (checkSolution(a1, b1, c1, a2, b2, c2))
        System.out.println("Yes");
    else
        System.out.println("No");
}
}
  
// This code is contributed by AnkitRai01

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Python3

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# Python3 program to find if two given 
# quadratic equations have common  
# roots or not 
  
# Function to check if 2 quadratic 
# equations have common roots or not. 
def checkSolution(a1, b1, c1, a2, b2, c2): 
      
    return ((a1 / a2) == (b1 / b2) and 
            (b1 / b2) == (c1 / c2))
  
# Driver code 
a1, b1, c1 = 1, -5, 6
a2, b2, c2 = 2, -10, 12
  
if (checkSolution(a1, b1, c1, a2, b2, c2)): 
    print("Yes"
else:
    print("No"
  
# This code is contributed by divyamohan123

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C#

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// C# Program to Find if two given
// quadratic equations have common 
// roots or not
using System;
class GFG{
      
// Function to check if 2 quadratic
// equations have common roots or not.
static bool checkSolution(float a1, float b1,
                          float c1, float a2,
                          float b2, float c2)
{
    return ((a1 / a2) == (b1 / b2) && 
            (b1 / b2) == (c1 / c2));
}
      
// Driver code
public static void Main (string[] args) 
{
    float a1 = 1, b1 = -5, c1 = 6;
    float a2 = 2, b2 = -10, c2 = 12;
          
    if (checkSolution(a1, b1, c1, a2, b2, c2))
        Console.WriteLine("Yes");
    else
        Console.WriteLine("No");
}
}
  
// This code is contributed by AnkitRai01

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Output:

Yes

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