diff --git a/book-example/src/format/mathjax.md b/book-example/src/format/mathjax.md
index 1f4db0d4..cc6a0b73 100644
--- a/book-example/src/format/mathjax.md
+++ b/book-example/src/format/mathjax.md
@@ -16,6 +16,6 @@ To indicate a block equation
 
 use
 
-```
+```bash
 \\[ \mu = \frac{1}{N} \sum_{i=0} x_i \\]
 ```