How can you determine if two lines are perpendicular?

Answer 1

find their slopes.
If the are the opposite reciprocals of each other, they are perpendicular.

or

if their product is -1 they are perpendicular.

Answer 2

thank you, But what if the product is something other than -1 Could it still be perpendicular? Why or Why not?

Answer 3

nope, if the product is not -1, they are not perpendicular

If the slopes are opposite reciprocals, their product will always be -1. So that is the basic condition.

e.g. slope of first = 4/5
slope of second = -5/4

(4/5)(-5/4) = -1

Answer 4

Thank you!