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# Parallel lines from equation (example 2)

Sal determines which pairs out of a few given linear equations are parallel. Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

• Two lines that are the same are not parallel, right?
• Alex,
You are correct. If two lines are the same line, then there is only one line, not two parallel lines.
• What is the difference between a parallel line and a perpendicular line?
• Parallel lines: \\ or || or // (they will never intersect with each other)
Perpendicular lines: 丄 (they intersect with each other, forming a right angle)
• Isn't B perpendicular to A or C?
• Chuck is right

Just a quick correction (to avoid possible confusion):
The slope for A and C is 3/4 , and the slope for B is -3/4
• How do I find the distance between two parallel lines?
• Choose a point on one of the lines (x1,y1).
The distance between the lines is then the perpendicular distance between the point and the other line. If you rewrite the equation of the line in standard form Ax+By=C, the distance can be calculated as:
|A*x1+B*y1-C|/sqroot(A^2+B^2).
It can also be calculated with slope-intercept form as:
|y1-(m*x1+b)|/sqrt(1+m^2)
• what does y intercept i.e b mean?
• A y-intercept is where a function intersects the y axis. That happens when x=0.
• The constants don't seem necessary in determining slope. Could we leave them out and calculate y = mx + (not needed) when determining parallel lines? What about for perpendicular lines?
• The constants are not necessary to determine the slope. Two lines are parallel when their slopes are the same, so constants are not needed then, unless you need to figure out if two different-seeming lines are in fact the same line, which some people may need in some circumstances. The Constants are important though if you plan to map either of the lines on a graph, so don't discard them entirely! :)
• 'Neither one of the other two'? isn't that a double negative?
• Yes, indeed it is. The subtitles say "either" instead of "neither" if anyone gets confused about the wording. Good thing this is a video on math, and not about grammar!
• I'm a little bit confused and want clarification.

If I have to answer a question, for example:

"Are the slopes given perpendicular,parallel, or neither?"

And the slopes given is m= 3/4 and m=-3/4,

My answer would have to be 'perpendicular', am I wrong?
• Yes, you're wrong. Perpendicular lines have negative reciprocal slopes, not merely negative slopes. Lines with slopes of 3/4 and -3/4 are neither parallel nor perpendicular.