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#1 2011-11-25 17:49:48

Registered: 2011-05-11
Posts: 171

Sufficient condition left out about parallel lines


"Parallel Lines

How do you know if two lines are parallel?

Their slopes are the same!"

The lines must also have different y-intercepts, else they are the
same line.

So, if you know that their slopes are the same, then you don't
(automatically) know if they are parallel lines or not.



On parallel vertical lines:

"a vertical line is parallel to another vertical line."

No, for example, x = -2 is a vertical line, and

3x + 6 = 0 is another vertical line.  These lines
are not parallel to each other because they are the
same line.

Distinct vertical lines are parallel to each other.

Last edited by reconsideryouranswer (2011-11-25 18:01:32)

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#2 2011-11-25 23:28:25

Registered: 2005-01-21
Posts: 7,663

Re: Sufficient condition left out about parallel lines

Thank you. Will review that page.

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman


#3 2012-05-25 10:46:04

Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

Re: Sufficient condition left out about parallel lines

Actually,tge definition of when two lines are parallel is when they are in the same plane and they do not intersect. I.e. A line is always parallel to itself.

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The knowledge of some things as a function of age is a delta function.


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