For this case we have to:
Given two lines:
[tex]y_ {1} = m_ {1} x_ {1} + b_ {1}\\y_ {2} = m_ {2} x_ {2} + b_ {2}[/tex]
By definition, if both lines are perpendicular to each other, then the product of their slopes is -1. That is to say:
[tex]m_ {1} * m_ {2} = - 1[/tex]
ANswer:
The product of the slopes of two perpendicular lines is -1.
