Newbie Help: Graphing Quad. Equations

[Kardafol]

I'm wondering if anyone has any idea how I should start making a XY graph, then plot a quadratic equation on it.

So far, I have the following (Solves the equation aslong as it's in a 'ax^2+bx+c=0' form)

class Quadratic
{
//varaibles
public $pat = '/^(-?[0-9.]*)x\^2([-+][0-9.]*)x([+-][0-9.]+)=0$/i';
public $a = 0;
public $b = 0;
public $c = 0;

function setABCByEquation($expr)
{
	if (preg_match($this->pat, $expr, $ans)) {
		$this->a = $ans[1];
		$this->b = $ans[2];
		$this->c = $ans[3];
		return $this->checkVars();
	} else
		return 0;
}
function setABCByValues($va = 1, $vb = 0, $vc = 1)
{
	$this->a = $va;
	$this->b = $vb;
	$this->c = $vc;
	return $this->checkVars();
}
function checkVars()
{
	if ($this->a == '-')
		$this->a = -1;
	else if ($this->a == 0)
		$this->a = 1;
	if ($this->b == '-') 
		$this->b = -1;	
	else if ($this->b == '' || $this->b == '+') 
		$this->b = 1;
	$this->b = ereg_replace("[^-0-9.]", "", $this->b);
	$this->c = ereg_replace("[^-0-9.]", "", $this->c);
	return 1;
}
function solve()
{
	if ($this->a == 0 || $this->c == 0) return 'err';
	$pre = sqrt(abs(($this->b*$this->b) - (4*$this->a*$this->c)));
	$ans[0] = (-$this->b + $pre) / (2 * $this->a);
	$ans[1] = (-$this->b - $pre) / (2 * $this->a);
	return $ans;
}
// Helper functions (clear();, getEquation()
}
/* Syntax:
$equation = new Quadratic();
$equation->setABCByEquation('x^2+4x+8=0');
$ans = $equation->Solve();
echo 'x = '.$ans[0].', '.$ans[1];
//Assuming no errors were found.
*/

As the equation is quadratic, the line should be smooth, and curve eather up or down.

I've never used the image functions with PHP, and I'm not quite sure where to start. It would be nice if someone could help me get started on this. 

[JasonLewis]

there is a person who made an awesome calculator, cant remember his/her name right now,that i think did this. is studied quadratics in maths and they would be hard to put on a graph in php. unless there is a seperate function for it.

 

if you go here, there is a list of all the image functions a tad way down the page:

http://au2.php.net/manual/en/ref.image.php

[hitman6003]

The first phpfreaks competition focused on creating a php based "graphing calculator".  I recommending checking out some of the submissions to that competition:

 

http://www.phpfreaks.com/forums/index.php/board,64.0.html

 

Specifically this page:

http://www.phpfreaks.com/forums/index.php/topic,115293.15.html

[Kardafol]

Thanks alot, I will check the links you provided. However I want to make it myself, I just get that feeling of acomplishment

[JasonLewis]

you can ask the creator on how they did it then expand it.