diff --git a/README.md b/README.md
index 6f05c7e..74f6425 100644
--- a/README.md
+++ b/README.md
@@ -2,3 +2,6 @@
 
 Gradient, Hessian etc
 https://pypi.org/project/numdifftools/
+
+Zadatak 3. 5)
+https://math.stackexchange.com/questions/1011563/norm-with-symmetric-positive-definite-matrix