diff --git a/notes/sections/4.md b/notes/sections/4.md
index db38cfd..2852479 100644
--- a/notes/sections/4.md
+++ b/notes/sections/4.md
@@ -100,8 +100,8 @@ where:
 $$
 \begin{cases}
   \arctan(P_h/P_v) &\incase P_v > 0 \\
-  \arctan(P_h/P_v) + \pi &\incase P_v < 0 \\
-  \pi/2 &\incase P_v = 0
+  \pi/2 &\incase P_v = 0            \\
+  \arctan(P_h/P_v) + \pi &\incase P_v < 0
 \end{cases}
 $$