Untitled

<?php
/**
 * Created by Alex Malyi.
 * User: https://vk.com/m1step
 * Git: https://github.com/m1step
 * Date: 20.10.2017
 */


/**
 * @param $first
 * @param $second
 * @param $third
 *
 * Поиск решения через дискриминант
 *
 * @return array|float|int|string
 */
function discriminant($first, $second, $third)
{
    $discriminant = pow($second, 2) - 4 * $first * $third;
    switch ($discriminant) {
        case $discriminant < 0;
            return 'Решений нет';
        case $discriminant == 0:
            return $second * (-1) / 2 * $first;
        default:
            $x1 = ($second * (-1) - sqrt($discriminant)) / 2 * $first;
            $x2 = ($second * (-1) + sqrt($discriminant)) / 2 * $first;
            return [
                'first_issue'  => $x1,
                'second_issue' => $x2
            ];
    }
}

/**
 * @param $first
 * @param $second
 * @param $third
 *
 *
 * @return array|float|int|string
 */
/*function vietta($first, $second, $third)
{
    $first_issue = false;
    $second_issue = false;

    $first_issue + $second_issue = $second / $first * (-1);
    $first_issue * $second_issue = $third / $first;

    return true;
}*/

/**
 * @param $arr string|integer|array
 */
function debug($arr)
{
    echo '<pre>' . print_r($arr, true) . '</pre>';
}

?>
<!DOCTYPE html><html lang="ru">
    <head>
        <meta charset="UTF-8">
        <title>Count</title>
    </head>
    <body>
        <form action="" method="POST">
            <label for="first_var">Первая переменная</label>
            <input type="number" name="first_var" id="first_var">
            <label for="second_var">Вторая переменная</label>
            <input type="number" name="second_var" id="second_var">
            <label for="third_var">Третяя переменная</label>
            <input type="number" name="third_var" id="third_var">
            <label for="checkbox">Посчитать виетта</label>
            <input type="checkbox" value="1" id="checkbox" name="boolean">
            <input type="submit" value="Посчитать">
        </form>
    </body>
</html>

<?php
if($_POST) {
    if (!isset($_POST['boolean'])) {
        debug(discriminant($_POST['first_var'], $_POST['second_var'], $_POST['third_var']));
    } else {
        debug('Здесь мы должны написать теорему Виета');
    }
}


?>