diff --git a/Mathematics/5th/Introduction_to_control_theory/Introduction_to_control_theory.tex b/Mathematics/5th/Introduction_to_control_theory/Introduction_to_control_theory.tex
index 234f7b8..7cfc034 100644
--- a/Mathematics/5th/Introduction_to_control_theory/Introduction_to_control_theory.tex
+++ b/Mathematics/5th/Introduction_to_control_theory/Introduction_to_control_theory.tex
@@ -161,7 +161,7 @@
       \begin{cases}
         \dot{\vf{x}} = \vf{f}(\vf{x}, \vf{u})         \\
         \dot{\vf{u}} = \vf\varphi(t, \vf{x}, \vf\chi) \\
-        \vf{\vf\chi} = \vf\psi(t, \vf{x}, \vf\chi)
+        \dot{\vf{\vf\chi}} = \vf\psi(t, \vf{x}, \vf\chi)
       \end{cases}
     $$
   \end{definition}