a) What is the slope of the line through the points (5, 2) and (5, -3)?
You asked the same type of question in #10 in
http://www.jiskha.com/display.cgi?id=1353965598
Can't you see the similarity of the two ?
slope = (-3-2)/(5-5) = -5/0
ahhh, a vertical line, thus the slope is undefined.