Is there a typo in b=[1, 2]^T? Shouldn’t it be b=[2, 1]^T? Thanks 
Yes! Absolutely. I think the mistake was found in class, through the lecture, but did not update it in the notes.
Now it is updated (assuming you refresh the page).
For those who have annotations already, on page II-113,
b ought to be [2, 1]^T, since the rows of A have also been interchanged from the original instance.