diff --git a/vektoren/serie_1_27.py b/vektoren/serie_1_27.py
index c5ece84..14e163f 100644
--- a/vektoren/serie_1_27.py
+++ b/vektoren/serie_1_27.py
@@ -54,7 +54,7 @@ d = Vector([1.0, 0.32])
 
 operations = [
     lambda: 4 * a + 2.1 * (b * c),
-    lambda: -8.35 * (a.cross(c) * b - abs(d) ** 2),
+    lambda: -8.35 * a.cross(c) * b - abs(d) ** 2,
     lambda: (3.1 * d).cross(a) - (a * 2 * c) * b,
     lambda: a * (1 / abs(d)) - (2 * b - 9.33 * c),
 ]
@@ -64,3 +64,28 @@ for operation in operations:
         print(operation())
     except Exception as e:
         print(f"Error: {e}")
+
+#%%
+import numpy as np
+
+a = np.array([3.8, 2.12, -4.01])
+b = np.array([0.01, -0.02, 2.341])
+c = np.array([-5.1, 1.0, 4.5])
+d = np.array([1.0, 0.32])
+
+# 4 * a + 2.1 * (b @ c) is mathematically not defined, but numpy will run it anyways, becaus it fills array fiels with 0. Native numpy can't catch this error
+operations = [
+    lambda: 4 * a + 2.1 * (b @ c),
+    lambda: -8.35 * np.cross(a, c) @ b - np.linalg.norm(d) ** 2,
+    lambda: np.cross(3.1 * d, a) - (a @ (2 * c)) * b,
+    lambda: a * (1 / np.linalg.norm(d)) - (2 * b - 9.33 * c),
+]
+
+for operation in operations:
+    try:
+        print(operation())
+    except Exception as e:
+        print(f"Error: {e}")
+
+
+# %%