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# In the xy-coordinate plane, line L and line K intersect at

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VP
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In the xy-coordinate plane, line L and line K intersect at [#permalink]

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10 Mar 2008, 11:52
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In the xy-coordinate plane, line L and line K intersect at point (4,3). Is the
product of their slopes negative?

(1) The product of the x-intercepts of lines L and K is positive.
(2) The product of the y-intercepts of lines L and K is negative.
Senior Manager
Joined: 15 Aug 2007
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10 Mar 2008, 18:53
C

Say the two lines are

L: x/a + y/b = 1 and K: x/c + x/d = 1

Slope of L = -b/a
Slope of K = -d/c

Product of slopes = bd/ac

Statement 1: ac>0 - Insufficient
Statement 2: bd<0 - Insufficient

Combined - bd/ac is negative.
VP
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15 Mar 2008, 02:18
sreehari wrote:
C

Say the two lines are

L: x/a + y/b = 1 and K: x/c + x/d = 1

Slope of L = -b/a
Slope of K = -d/c

Product of slopes = bd/ac

Statement 1: ac>0 - Insufficient
Statement 2: bd<0 - Insufficient

Combined - bd/ac is negative.

I reasoned in this way:

1. y=c/a and y1=k/d; ck/ad>0 where c and k are the constants. it doesn't say much
2. ck/be<0 alone insuff

together it's clear that ad and be have different signs so c is suff

anyway, it took me far more than 2 minutes to solve this one and would like to know if there is any shortcut. moreover, why does the argument tell us that the intersection point is 4,3?
thanks
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Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
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15 Mar 2008, 22:21
marcodonzelli wrote:
moreover, why does the argument tell us that the intersection point is 4,3?
thanks

I think to help solve the problem with drawing.
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VP
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Kudos [?]: 567 [0], given: 0

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16 Mar 2008, 00:50
walker wrote:
marcodonzelli wrote:
moreover, why does the argument tell us that the intersection point is 4,3?
thanks

I think to help solve the problem with drawing.

yes, drawing would help solve this problem in 1 minute.
Re: gmatprep coordinate geo   [#permalink] 16 Mar 2008, 00:50
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