diff --git a/docs/reference/math.md b/docs/reference/math.md
index bb832d736..83cc8df37 100644
--- a/docs/reference/math.md
+++ b/docs/reference/math.md
@@ -138,14 +138,14 @@ lines:
 
 ``` latex title="block syntax"
 $$
-\operatorname{ker} f=\{g\in G:f(g)=e_{H}\}{\mbox{.}}
+\cos x=\sum_{k=0}^{\infty}\frac{(-1)^k}{(2k)!}x^{2k}
 $$
 ```
 
 <div class="result" markdown>
 
 $$
-\operatorname{ker} f=\{g\in G:f(g)=e_{H}\}{\mbox{.}}
+\cos x=\sum_{k=0}^{\infty}\frac{(-1)^k}{(2k)!}x^{2k}
 $$
 
 </div>