Untitled

<?php

if(isset($_POST['nilai'])){
  function first($x)
  {
    $a = pow($x,3) + 2*pow($x,2) + 10*$x - 20;
    return $a;
  }

  function turunan_first($x){
    $a = 3*pow($x,2) + 4*$x + 10;
    return $a;
  }

  function hasil_1($x)
  {
    $per = first($x) / turunan_first($x);
    $a = $x - $per;

    return $a;
  }


}

 ?>
 <!DOCTYPE html>
 <html lang="en" dir="ltr">
   <head>
     <meta charset="utf-8">
     <title>Metode Numerik</title>
     <style media="screen">
     body{
       background: #fdfafa;
     }
       form{
         width: 30%;
         height: auto;
         margin:auto;
         padding:32px;
         border:1px solid #f1f1f1;
         box-shadow: 2px 1px 8px #d9d9d9;
         border-radius:4px;
         margin-top:250px;
         background: #fff;
       }
       input{
         padding:4px;
       }
       button{
         background: #07c;
         color:#fff;
         border:2px solid #07c;
         padding:4px 38px;
         border-radius:2px;
       }
     </style>
   </head>
   <body>
     <form action="index.php" method="post">
       <label for="">Masukkan Nilai : </label>
       <input type="text" name="nilai" value="">
       <button type="submit" name="button">Cek</button>
     </form>
     <table align="center" border="1" width="800">
       <tr>
         <th>Iterasi</th>
         <th>F(x)</th>
         <th>F'(x)</th>
         <th>g(x)</th>
         <th>Error(x)</th>
       </tr>
     <?php
     $flag = true;
     $i = 1;
     $x = $_POST['nilai'];
     $givenError = $x;

      while ($flag) {
        $root = hasil_1($x);
        $error = abs(($root - $x)/$root)*100;
        $f = first($x);
        $f0 = turunan_first($x);
      ?>
      <tr>
        <td><?= $i++ ?></td>
        <td><?= number_format($f,6) ?></td>
        <td><?= number_format($f0,6) ?></td>
        <td><?= number_format($root,6) ?></td>
        <td><?= number_format($error,6) ?></td>
      </tr>

      <?php
        $x = $root;

        if($givenError > $error){
          $flag = false;
        }
      }
      ?>
      </table>
   </body>
 </html>