Basic javascript solving quadratic equations

Question

Very new programmer, trying to make a quadratic equation solver in javascript.

//QuadSolver, a b c as in classic ax^2 + bx + c format
function quadsolve(x, a, b, c) {
  var sol = (
    ((a * (x * x)) + (b * x)) + c
    )
}
//Test
console.log(quadsolve(1, 1, 1, 0))

In the console, it outputs "undefined". Would this be the correct way to go about solving the problem? If so, how would I get a value instead of undefined? Thanks!

You don't return anything from the function, so there is an implicit return of `undefined`. Also note that isn't the *solution* for a quadratic expression...https://en.wikipedia.org/wiki/Quadratic_equation — Jared Smith, Dec 20 '20 at 18:37
What are you trying to solve for? You're given all the values. — Musa, Dec 20 '20 at 18:39
To give an example of what Jared write: before `}` in the method, type "return sol". — Rickard Elimää, Dec 20 '20 at 18:46
The return worked, thanks! And I was trying to solve for y in this equation — Hikatchus, Dec 21 '20 at 01:37

score 0 · Answer 1 · answered Feb 14 '21 at 06:41

Like the others said you need to use the "return" keyword to return a value. Are you trying to find the zeros of the equation? If so here is the numeric solution:

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<script src="https://polyfill.io/v3/polyfill.min.js?features=es6"></script>
<script id="MathJax-script" async
        src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js">
</script>
</head>
<body>

<h2>Quadratic Equation</h2>
<p>This is an example of the numerical solution of a quadratic equation using <a href="https://github.com/Pterodactylus/Ceres.js">Ceres.js</a></p>
<p>
Problem Statment: find x when \(f(x)=0\)
\[f(x) = a*x^2+b*x+c\]

</p>

<textarea id="demo" rows="40" cols="170">
</textarea>

<script type="module">
    import {Ceres} from 'https://cdn.jsdelivr.net/gh/Pterodactylus/Ceres.js@master/Ceres-v1.5.3.js'

    var fn1 = function(x){
    let a = 1
    let b = -1
    let c = 1
        return a*x[0]*x[0]+b*x[0]+c //this equation is of the form f(x) = 0 
    }
    
    let solver = new Ceres()
    solver.add_function(fn1) //Add the first equation to the solver.
    
    solver.promise.then(function(result) { 
        var x_guess = [1] //Guess the initial values of the solution.
        var s = solver.solve(x_guess) //Solve the equation
        var x = s.x //assign the calculated solution array to the variable x
        document.getElementById("demo").value = "The solution is x="+x+"\n\n"+s.report //Print solver report
        solver.remove() //required to free the memory in C++
    })
</script>
</body>
</html>

Basic javascript solving quadratic equations

1 Answers1