Solve Quadratic Equation in JavaScript

This tutorial explains how to find the square root of a number in JavaScript. In JavaScript, we use

JavaScript if...else Statement
JavaScript Math sqrt()

Standard Form

The standard form of a quadratic equation is:

ax2 + bx + c = 0

where a, b and c are real numbers and a ≠ 0

To find the roots of such equation, we use the formula,

(root1,root2) = (-b ± √b^2-4ac)/2a

The discriminant of the quadratic equation is D = b2 - 4ac

For D > 0 the roots are real and distinct.

For D = 0 the roots are real and equal.

For D < 0 the roots do not exist, or the roots are imaginary.

Example

let quadEquation = function (a, b, c) {
  let discriminant = Math.sqrt( (b * b) - (4 * a * c) );
  let denom = 2 * a;
  let firstRoot,secondRoot;
  
  if (discriminant>0){
    firstRoot = (-b + discriminant)/denom;
    secondRoot = (-b - discriminant)/denom;
  }
  else if (discriminant == 0){
      firstRoot = secondRoot = -b/denom;
  }
  else{
    let real = (-b / denom ).toFixed(2);
    let imag = (Math.sqrt(-discriminant) / denom ).toFixed(2);
    
    let firstRoot = `${real} + ${imag}i`
    let secondRoot = `${real} - ${imag}i`
  }
  
  console.log("The first root is " + firstRoot);
  console.log("The second root is " + secondRoot);
};

quadEquation(5,6,1)

Output

The first root is -0.2
The second root is -1