Math
posted by Diana .
How can you determine if two lines are perpendicular?

find their slopes.
If the are the opposite reciprocals of each other, they are perpendicular.
or
if their product is 1 they are perpendicular. 
thank you, But what if the product is something other than 1 Could it still be perpendicular? Why or Why not?

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 
Thank you!