<h2>select shape</h2>
<p>
Please select shape to calculate the area of rectangle or tringle and press submit...
<p>

<form method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>">
   <br><input type="radio" name="shape" value="Rectangle" /> Rectangle
<br><input type="radio" name="shape" value="Tringle" /> Tringle
<input type="submit" name="submit" value="Submit Form"><br>
</form>

<?php
   echo("<br>");
        if (isset($_POST['submit'])) {
          if (!empty($_POST['shape'])) {
        if (!empty($_POST['Rectangle'])) { echo "You got Rectangle answer!"; }
          else { echo "You got Tringle answer!"; }
      }
  }
  ?>