diff --git a/index.html b/index.html
index 968fac6..8135a84 100644
--- a/index.html
+++ b/index.html
@@ -21,7 +21,7 @@
   function minus(a, b) {
     return a-b;
   }
-  
+
   function pow(a, b) {
     return Math.pow(a, b);
   }
@@ -29,6 +29,10 @@
   function abs(a) {
     return Math.abs(a);
   }
+  
+  function cos(a) {
+    return Math.cos(a)
+  }
 </script>
 </body>
 </html>