GMAT Prep Coordinate Geometry

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ankanas: Junior | Next Rank: 30 Posts; Posts: 20; Joined: Thu May 24, 2007 3:44 pm

by ankanas » Thu Aug 30, 2007 11:04 pm

Anyone?

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Source: Beat The GMAT — Data Sufficiency | Thu Aug 30, 2007 11:04 pm

Bharat: Senior | Next Rank: 100 Posts; Posts: 70; Joined: Sun Jul 22, 2007 11:43 pm; Thanked: 8 times

by Bharat » Fri Aug 31, 2007 1:04 am

Hi,
I believe that the answer is E (because the angle between the two lines cant be decided based upon given information.)
Note that if line K passes through (1, 1) & (1, -1) then it will always pass through (1,0)

Hence both points 1 & 2 are the same piece of information, These elaborate information about line K only.
However no information is provided about line M & its angle with line K

1. All we know about line M is that it passes through (1, -1) which is intersection point, & the angle of intersection cant be decided.
NOT SUFFICIENT

2: this information is again the same as 1 only except that it provides K's intersection point with X axis.
NOT SUFFICIENT

Even after combining 1 & 2, we do not get any additional information. Hence E.

Let me know if I missed anything.

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agps: Master | Next Rank: 500 Posts; Posts: 101; Joined: Tue Aug 07, 2007 1:45 amFollowed by: 1 member

by agps » Fri Aug 31, 2007 1:41 am

I agree with Bharat, there seeems thata there is not enough information, so answer should be E.
anyone has any lights on this?

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kajcha: Master | Next Rank: 500 Posts; Posts: 321; Joined: Tue Aug 28, 2007 5:42 am; Thanked: 1 times

by kajcha » Fri Aug 31, 2007 5:57 am

IMO Should be E

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ankanas: Junior | Next Rank: 30 Posts; Posts: 20; Joined: Thu May 24, 2007 3:44 pm

by ankanas » Fri Aug 31, 2007 6:09 am

Thanks Bharat..

Please tell me how did you come to the conclusion that if line K passes through (1, 1) & (1, -1) then it will always pass through (1,0)..

I am stumped when it comes to coordinate geometry..

Thanks

Ankana

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agps: Master | Next Rank: 500 Posts; Posts: 101; Joined: Tue Aug 07, 2007 1:45 amFollowed by: 1 member

by agps » Fri Aug 31, 2007 6:56 am

if a line passes through (1,1) and (1,-1) it's equation is x=1, therefore it should pass through (1,x).
draw this and you see why.
if you want a math explanation,

y = mx+b
m=(y2-y1)/(x2-x1) in this case infinite (x2-x1 = 0).
this a case of a vertical line, where x always takes the same value, from the two points you see that the value is one, therefore the equation is x=1 (x is one for all values of y).

if m was 0 the line would be horizontal and you would get y=a line equation (a the value of y for any value of x)

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ankanas: Junior | Next Rank: 30 Posts; Posts: 20; Joined: Thu May 24, 2007 3:44 pm

by ankanas » Fri Aug 31, 2007 7:32 am

Thanks agps

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Bharat: Senior | Next Rank: 100 Posts; Posts: 70; Joined: Sun Jul 22, 2007 11:43 pm; Thanked: 8 times

by Bharat » Fri Aug 31, 2007 8:51 pm

Thanks Agps,

Just to add, in case of any lines, try to draw a rough sketch of the the points. It will show where the lines might intersect.

For a line you need to know only 2 pieces of information:
1. Any two points through which the line passes.
2. one point through which the line passes + one angle with some other known line.

I believe this will help in future questions.
Let me know if more details are needed.

Thanks,
Bharat.

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