Which of the following 2 lines are perpendicular to each other?

a) 2x + 1

b) -3x + 4

c) -x – 3

d) x + 2

Perpendicular lines have slopes that are negative reciprocals of each other.

This is only true of line (a) with the slope=2 and line (c ) with the slope= - , so they are perpendicular to each other.