diff --git a/index.html b/index.html
index 8135a84..5f9bb81 100644
--- a/index.html
+++ b/index.html
@@ -29,10 +29,14 @@
   function abs(a) {
     return Math.abs(a);
   }
-  
+
   function cos(a) {
     return Math.cos(a)
   }
+
+  function tan(a) {
+    return Math.tan(a);
+  }
 </script>
 </body>
 </html>