<?php

$a = 1;
$b = 3;
$c = -4;
$d = $b ^ 2 - 4 * $a * $c;
$y = -$b / 2 * $a;
$x1 = ((-$b) - sqrt($d)) / 2 * $a;
$x2 = ((-$b) + sqrt($d)) / 2 * $a;

if ($d<0) {
    echo 'no real roots';
} elseif($d==0){
    echo $y;
} else {
    echo $x1;
}