## Problem 1 Critique

a) and b) are as same as mine which I think are probably correct

For part c), the solution is almost the same just need to follow what the instruction said in terms of $ \lambda_n $, $ \lambda_n^b $, and $ \lambda_n^d $

For part d). I am not sure what the correct curve should be.

## Problem 2 Critique

For this problem, I consider that part b is not the correct way to prove positive semi-definite. To prove a matrix A is p.s.d, need an arbitrary vector x and prove that$ x^tAx \geq 0 $. Prove $ \Sigma^2 \geq 0 $ is not enough.