Question

tell whether each pair of lines is parallel, perpendicular, or neither: y=2x-1 and y=1/2x+2

Answer 1

neither.. draw the graph then you will see

Answer 2

if you don't want to draw (but I suggest you do to convince yourself), you can look at the slope of each line and compare.

if the slopes are equal they are parallel (or the same line).
if the slopes are opposite and reciprocals of each other, then they are perpendicular.