Question

For any pair of perpendicular lines the product of the slope is always

Answer 1

Theorem 105: If two nonvertical linesare perpendicular, then their slopes are opposite reciprocals of one another, or the product of their slopesis −1. ... Horizontal and vertical linesare always perpendicular: therefore, two lines, one of which has a zeroslope and the other an undefined slopeare perpendicular.