SOLUTION: when i am trying to get a line that is parallel to a line that is going through a set of given points, when do i use the rule that tells me to use opposite sign and flip the number

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Question 8791: when i am trying to get a line that is parallel to a line that is going through a set of given points, when do i use the rule that tells me to use opposite sign and flip the number upside down in my equation?
Answer by Earlsdon(6287) (Show Source):
You can put this solution on YOUR website!
You seem to be talking about slopes.But remember, parallel lines have identical slopes.
Perpendicular lines, on the other hand, have slopes the are the negative reciprocal (or, as you put it "...use opposite sign and flip the number upside down...") of each other.
So, the answer is: Do it when you have perpendicular lines, not when you have parallel lines