Posted by **Diana** on Thursday, June 17, 2010 at 10:29pm.

How can you determine if two lines are perpendicular?

- Math -
**Reiny**, Thursday, June 17, 2010 at 10:47pm
find their slopes.

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

or

if their product is -1 they are perpendicular.

- Math -
**Diana**, Thursday, June 17, 2010 at 10:50pm
thank you, But what if the product is something other than -1 Could it still be perpendicular? Why or Why not?

- Math -
**Reiny**, Thursday, June 17, 2010 at 11:12pm
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

- Math -
**Diana**, Thursday, June 17, 2010 at 11:39pm
Thank you!

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