Comments on 27

average of 75, 23 submitted, 20 points for each problem.

online problem was good.

4-2 was decent. Some people didnt use summations when they should have and this
made their work quite incoherent.

4-3 was good.

4-5 was not so good. The answer is as follows:

Clearly lambda is zero and the eigenvectors span Rn. So A times any eigenvector
is zero, and hence A times any lin comb of the eigenvectors is zero, and so A
times any vector in Rn is zero, ie A is zero. QED.

4-6 was pretty good. Some alebraic mistakes bur few or no conceptual ones.