# Do two equal lines also count as intersecting?

So, I asked a question about how to find if three lines are concurrent. I built the algorithm I needed, and it was working well, until I started doubting my power of judgement. So my question:

Are two equal lines also intersecting?

For an example, $9x+9y=9$; $7x+7y+7$ ? Because now, if I would draw these lines and add any line to the comparison, these three lines would be concurrent.

help?

-
Yes; they intersect at all of their points. – Qiaochu Yuan Sep 23 '10 at 20:46
NOTE If you have 2 equal lines L, then it's not true that any 3rd line works since it won't intersect L if it's parallel to L. But once you have 2 equal lines L the problem reduces to a simpler one: if any other line intersects L then that gives your point of multiplicity 3; else all lines are parallel to L and you need only check if there are 3 equal lines. – Bill Dubuque Sep 23 '10 at 21:12
The answer to your question really depends on whether you want coincident lines to be intersecting or not! – Mariano Suárez-Alvarez Sep 24 '10 at 7:41
@Janis, then you should be asking him. – Mariano Suárez-Alvarez Sep 24 '10 at 8:25
But you'd b asking your teacher: by asking him questions (and no, this is not a stupid question) it is precisely that you are supposed to get that sort of background!!!! – Mariano Suárez-Alvarez Sep 24 '10 at 23:25