Which set of lines is perpendicular?
the line between the points (7,4) and (4,7), and the line between the points (3,9) and (4,8)
the line between the points (1,3) and (3,5), and y = 4_x_ + 7
y = x – 1/2 and y = –x + 1/2
y = 3_x_ + 5 and y = 5_x_ + 3
y = 3_x_/5 – 3 and y = 5_x_/3 + 3
