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arocks: Master | Next Rank: 500 Posts; Posts: 127; Joined: Tue Oct 02, 2007 9:35 am; Thanked: 1 times

by arocks » Sat Oct 13, 2007 1:19 am

In the xy-coordinate plane, line l and k intersect at the 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

Pls explain. Thanks.

OA - C[/spoiler]

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Source: Beat The GMAT — Data Sufficiency | Sat Oct 13, 2007 1:19 am

camitava: Legendary Member; Posts: 645; Joined: Wed Sep 05, 2007 4:37 amFollowed by: 5 members; Location: India; Thanked: 34 times

by camitava » Sat Oct 13, 2007 1:33 am

arocks,
Slop = y-intercept/ x-intercept
say y-intercept of l and k be y1 and y2
x-intercept of l and k be x1 and x2

So m1 * m2 = (y1 * y2) / (x1 * x2)

So to find out whether m1 * m2 < 0, we have to know the fact whether both (x1 * x2) and (y1 * y2) are < 0 or not. So C is the answer to chose.

Correct me If I am wrong

Regards,

Amitava

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arocks: Master | Next Rank: 500 Posts; Posts: 127; Joined: Tue Oct 02, 2007 9:35 am; Thanked: 1 times

by arocks » Sat Oct 13, 2007 1:39 am

Thanks.

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