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# Coordinate Geometry

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Senior Manager
Joined: 20 Feb 2008
Posts: 296
Location: Bangalore, India
Schools: R1:Cornell, Yale, NYU. R2: Haas, MIT, Ross
Followers: 4

Kudos [?]: 38 [0], given: 0

Coordinate Geometry [#permalink]  04 May 2008, 13:52
Could you please provide an explanation for this question, I think I am missing an obvious point here.
Thank you.
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GMAT Prep 1 Coordinate Geometry.doc [112 KiB]

VP
Joined: 10 Jun 2007
Posts: 1464
Followers: 6

Kudos [?]: 142 [0], given: 0

Re: Coordinate Geometry [#permalink]  04 May 2008, 14:12
ventivish wrote:
Could you please provide an explanation for this question, I think I am missing an obvious point here.
Thank you.

C for me.

L = m1*x + b1
K = m2 *x + b2

We want to find if m1*m2<0 ?

(1) is given that product of x intercepts is positive
To find x-intercept, set y=0.
For line L: x = -b1/m1
For line K: x = -b2/m2
So we know that
(b1/m1)*(b2/m2) >0
In this case, we don't know b1 or b2, so INSUFFICIENT

(2) is given that product of y intercepts is negative
To find y-intercept, set x=0
For line L: y = b1
For line K: y = b2
So we know that
b1*b2 < 0
Don't know anything about slopes, INSUFFICIENT

Together, we know that
(b1*b2) / (m1*m2) > 0 AND b1*b2 < 0
This means that
m1 * m2 must be negative.
SUFFICIENT
Senior Manager
Joined: 20 Feb 2008
Posts: 296
Location: Bangalore, India
Schools: R1:Cornell, Yale, NYU. R2: Haas, MIT, Ross
Followers: 4

Kudos [?]: 38 [0], given: 0

Re: Coordinate Geometry [#permalink]  04 May 2008, 16:07
Thank you !!!Makes sense now.
Re: Coordinate Geometry   [#permalink] 04 May 2008, 16:07
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