fix math

_includes/head.html

@@ -30,4 +30,17 @@
 
   <!-- Styles -->
   <link rel="stylesheet" href="{{ site.baseurl }}/css/index.css">
-</head>
+
+  <!-- MathJax -->
+  <script type="text/x-mathjax-config">
+    MathJax.Hub.Config({
+      tex2jax: {
+        inlineMath: [ ['$','$'], ["\\(","\\)"] ],
+        processEscapes: true
+      }
+    });
+  </script>
+  <script src='https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.5/MathJax.js?config=TeX-MML-AM_CHTML' async></script>
+  </script>
+
+</head>