added missing custom raise exception

content/Week_1_6/PA/PA6-Challenges_A.py

@@ -30,4 +30,6 @@ plt.show()
 
 
 if not (numerical_integral_trap - numerical_integral_simp)/numerical_integral_simp < 0.3:
-    raise ValueError('The difference between the two methods is too high! ')
\ No newline at end of file
+    raise ValueError('The difference between the two methods is too high! ')
+if numerical_integral_simp < 0 and numerical_integral_trap < 0:
+    raise ValueError('The results should be positive!')