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

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There are two lines with slopes m and n. Are they [#permalink]  31 Mar 2008, 13:36
There are two lines with slopes m and n. Are they perpendicular?

1. mn =-1
2. m > 0 and n < 0
Intern
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Re: Coordinate geometry [#permalink]  31 Mar 2008, 13:50
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
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Re: Coordinate geometry [#permalink]  31 Mar 2008, 17:07

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
Re: Coordinate geometry   [#permalink] 31 Mar 2008, 17:07
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