diff --git a/4 Qualifying Exam/3 Notes/Feedback Control Theory.md b/4 Qualifying Exam/3 Notes/Feedback Control Theory.md
index 9bce832a9..03c5912a1 100644
--- a/4 Qualifying Exam/3 Notes/Feedback Control Theory.md	
+++ b/4 Qualifying Exam/3 Notes/Feedback Control Theory.md	
@@ -90,7 +90,10 @@ W_2 is basically a transfer function that will always be greater in magnitude th
 >[!note] Robustness
 >A controller $C$ is robust to set of plants $\mathcal{P}$ with respect to a characteristic if this characteristic holds for every plant in $\mathcal{P}$. 
 >> [!important] Robust Stability
->> A system is robustly stable if it is internally stable for every plant in the set $\mathcal{P}$.
+>> A system is robustly stable if it is internally stable for every plant in the set $\mathcal{P}$:
+>> $$|| \Delta W_2 T ||_\infty < 1$$
+
+
 >>