diff --git a/00004_optimalization-quadratic_function/en_article_proofreading.md b/00004_optimalization-quadratic_function/en_article_proofreading.md
index ee2d773..f7148fe 100644
--- a/00004_optimalization-quadratic_function/en_article_proofreading.md
+++ b/00004_optimalization-quadratic_function/en_article_proofreading.md
@@ -48,11 +48,11 @@ the arithmetic mean of the real roots of a quadratic polynomial (assuming
 that they exist). We will determine these roots now:
 
 $$
-\begin{align*}
+\begin{aligned}
 -5\ 000x^2 + 5\ 000x + 60\ 000 &= 0 \\
 x^2  - x - 12 &= 0\\
 (x-4)(x+3)&=0
-\end{align*}
+\end{aligned}
 $$
 
 The roots of the quadratic equation are $x_1=4$ and $x_2=-3$, therefore the maximum of the function $f$ is