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There are two lines with slopes m and n. Are they

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Intern
Joined: 19 Mar 2007
Posts: 18

Kudos [?]: 3 [0], given: 0

There are two lines with slopes m and n. Are they [#permalink]

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31 Mar 2008, 14:36
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

There are two lines with slopes m and n. Are they perpendicular?

1. mn =-1
2. m > 0 and n < 0

Kudos [?]: 3 [0], given: 0

Intern
Joined: 31 Mar 2008
Posts: 14

Kudos [?]: 1 [0], given: 0

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31 Mar 2008, 14:50
There are two lines with slopes m and n. Are they perpendicular?

1. mn =-1

m = -1/n
slope of m is the negative reciprocal of n. negative reciprocals are perpendicular.

2. m > 0 and n < 0

irrelevant

Only (1) is needed

Kudos [?]: 1 [0], given: 0

Senior Manager
Joined: 01 Feb 2005
Posts: 271

Kudos [?]: 109 [0], given: 1

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31 Mar 2008, 18:07

There are two lines with slopes m and n. Are they perpendicular?

1. mn =-1
2. m > 0 and n < 0

From 1 we know that the product of slopes = -1. Therefore 1 is sufficient (AD)

2 is insufficient M could be 1 and n could be -1. Therefore m.n = -1 (Perpendicular) But what if m = 2 and n = -1 (insufficient).

Hence A is the best answer

Kudos [?]: 109 [0], given: 1

Re: Coordinate geometry   [#permalink] 31 Mar 2008, 18:07
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