diff --git a/index.html b/index.html
index 5eca14e..6b13f09 100644
--- a/index.html
+++ b/index.html
@@ -38,9 +38,14 @@
   function sin(a) {
     return Math.sin(a);
   }
+
   function asin(a) {
     return Math.asin(a);
   }
+
+  function acos(a) {
+    return Math.acos(a);
+  }
 </script>
 </body>
 </html>