<!DOCTYPE html>
<html>
<body>

<form>
  Base:<br>
  <input type="text" id="base" name="base"><br>
  Height:<br>
  <input type="text" id="height" name="height"><br>
  <br>
  <button type="button" onclick="calculateArea()">Calculate Area</button>
  <br><br>
  Area: <span id="result"></span>
</form>

<script>
function calculateArea() {
  var base = document.getElementById("base").value;
  var height = document.getElementById("height").value;
  var area = (base * height) / 2;
  document.getElementById("result").innerHTML = area;
}
</script>

</body>
</html>
Kendinize göre değişkenlerinin ismini değiştirebilirsiniz.