Slopes of Parallel + Perpendicular Lines

Question

Which lines are perpendicular? Explain your reasoning.

Question 1:

X=0, Y=3

Question 2:

Y=2, Y= -1/2

Answer 1

Question (1) has a line of constant x, which is a vertical line, and a line of constant y, which is a horizontal line. These two lines are perpendicular.

Question (2) has two lines of constant y, which are parallel lines.