Following the hint, A(:, 3) returns the third column of matrix A {\displaystyle A} :
[ 3 1 7 ] {\displaystyle \color {blue}\left[{\begin{array}{ccclc}3\\1\\7\\\end{array}}\right]}
![{\displaystyle \color {blue}\left[{\begin{array}{ccclc}3\\1\\7\\\end{array}}\right]}](https://wiki.ubc.ca/api/rest_v1/media/math/render/svg/588cc2ed647756d61d5d4d3e6305f6544893afad)