Question: what is the slope when a line is perpendicular?
Answer: Perpendicular Lines and Slopes The slopes of two perpendicular lines are negative reciprocals of each other. This means that if a line is perpendicular to a line that has slope m, then the slope of the line is -1 / m. For example, we found that the slope of the line y = (1/2)x + 3 is 1/2.