public function __equationToString()
    {
        $str = '';
        $a = $this->getSlope();
        if ($a!=1) {
            $str .= "({$a} * x)";
        } else {
            $str .= "x";
        }
        $b = $this->getYIntercept();
        if ($b!=0) {
            $str .= " + {$b}";
        }
        return "y = f(x){ {$str} }";
    }