I can't reproduce what you're reporting: https://3v4l.org/fnd5R

Please can you provide an actual runnable reproduce script.

You are right: the problem can't be reproduced in a testbed for PHP 5.6.30. I suppose there is a problem in realization (librariess are compiled against musl libc on Alpine Linux) or a hardware issue...
Thank you danack at php dot com
<?php
  $start = 60.0;
  $a = $start;
  $da = 0.1;
  $target = M_PI + $start;
  $tab = array();
  while ($a < $target) {
    $item['rad'] = $a;
    $item['deg'] = number_format(rad2deg($a), 2);
    $item['sin'] = sin($a);
    $item['cos'] = cos($a);
    $tab[] = $item;
    $a += $da;
  }
?>
<style>
table, td, th {
  border-collapse:collapse;
  border:1px solid #000;
}
</style>
<table>
  <tr>
    <th>Radian</th>
    <th>Degrees</th>
    <th>Sin</th>
    <th>Cos</th>
  </tr>
  <?php foreach($tab as $item): ?>
    <tr>
      <td><?= $item['rad'] ?></td>
      <td><?= $item['deg'] ?></td>
      <td><?= $item['sin'] ?></td>
      <td><?= $item['cos'] ?></td>
    </tr>
  <?php endforeach; ?>
</table>

Does a simple
  #include <math.h>
  #include <stdio.h>
  void main(void) { printf("%f\n", sin(60.0)); }
work correctly?

Standard libc sin() works just fine. Bc also gives correct result on the machine in question:
echo 's(60)' | bc -l

But problem with php is still there:
php5 -r 'echo sin(60) . "\n";'
output is 19880855899899

Right now I use a workaround
echo sin(fmod(60, M_PI * 2));

PS: Seems like this is not a hardware issue, neither musl libc. Result is always the same even after restarting php5-fpm. Alpine Linux uses grsec patch and loads binaries in arbitrary memory addresses on each start.
I additionally posted a bug report on Alpine Linux board.

No feedback was provided. The bug is being suspended because
we assume that you are no longer experiencing the problem.
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change the status of the bug back to "Re-Opened". Thank you.