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Slope of line

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Slope of line

by erjamit » Wed Jul 16, 2008 11:12 am
Hi,

In the xy-plane, what is the slope of line l?
(1) Line l dose not intersect the line with equation y = 1 - x.
(2) Line l intersects the line with equation y = x – 1.

Can someone pls explain.

source is old gmat sets

Thanks
Amit




OA is A
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by Canman » Wed Jul 16, 2008 5:14 pm
1) If line l does not intersect, then it must be parallel (i.e. same slope) -- SUFFICIENT

2) Tells us nothing about HOW it intersects (e.g., perpendicular or some other angle created by the intersection) -- NOT SUFFICIENT

Hope this helps.
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by Canman » Wed Jul 16, 2008 5:19 pm
1) If line l does not intersect, then it must be parallel (i.e. same slope) -- SUFFICIENT

2) Tells us nothing about HOW it intersects (e.g., perpendicular or some other angle created by the intersection) -- NOT SUFFICIENT

Hope this helps.
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by erjamit » Wed Jul 16, 2008 9:29 pm
I don't know what I was thinking while solving this. It is so simple.

Thanks
Amit
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by wilderness » Thu Jul 17, 2008 12:15 am
Canman wrote: 2) Tells us nothing about HOW it intersects (e.g., perpendicular or some other angle created by the intersection) -- NOT SUFFICIENT
Hi Canman,

I agree with your answer but I have one question about the second part. If it was a perpendicular, its clear that the slope of the second line would be such that the product is -1. But what if we are given that lines interest at some angle other than 90. e.g. 60. Would that be sufficient ? I think not, because it could be 60 clockwise or 60 anticlockwise.

Taking it a step further, if we get a question like this in PS and that we have actually to calculate the slop of a line that makes an angle of 60 degrees clockwise with y = x – 1, how can we calculate this ? One idea I could think of was drawing a perpendicular from the given line to the new line. Then we have a rt angled triangled for which we know all angles. We can now try to calculate this way. But is there an easier way.

Sorry for so many questions together.

Thanks for a kind reply.

BR,
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by Canman » Thu Jul 17, 2008 10:35 am
Slopes and angles are related so you should be able to use one to help determine another one if given enough information.

Sounds like to find the slope of intersecting line you suggest we may be able to take the slope given and multiply by x/90 where x is degree angle created by the intersection. I don't know for certain if this works all the time but it seems reasonable.

Anyone else have any input?
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by manishpal » Sun Sep 18, 2011 2:54 am
good question
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by eski » Tue Sep 18, 2012 10:04 am
slope is a measure of the angle of a line from the horizontal, and since parallel lines must have the same angle, then parallel lines have the same slope - and lines with the same slope are parallel

-eski
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