The common errors on Assign 1 are as follows:

1. In Question 1.1.b, most of the student didn't say anything about the test of global min. 1 mark was taken off here.
2. In Question 1.2.a, and in general, some students have difficulty with the second order conditions. They argued that because the second derivative takes both negative and positive values, we do not have global min and max.
3. Many students had difficulty with question 3 (second order conditions.). They didn't understand that if the Hessian is positive semi-definite at a point, we can not decide on local minimality or maximality. Some others had problems with 'locality'. They took the function values at points like (1,0) or (2,2) and then tried to argue by using them.