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

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Manager
Joined: 31 Jul 2006
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In the xy coordinate plane, line l and line k intersect at [#permalink]

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11 Oct 2008, 01:03
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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?
a. The product of the x intercepts of line l and line k is positive
b. The product of the y intercepts of line l and line k is negative

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Senior Manager
Joined: 21 Apr 2008
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13 Oct 2008, 16:32
In the xy coordinate plane, line l and line k intersect at point (4,3). Is the product of their slopes negative?
a. The product of the x intercepts of line l and line k is positive
b. The product of the y intercepts of line l and line k is negative

L -> Y = m1 X + C1
K -> Y = m2 X + C2
Point (4,3) is on both lines
4m1+C1 = 3
4m2+C2 = 3

Is m1*m2 Positive ?

a. X Intercept is calculated when Y = 0
-C1/m1 * - C2/m2 is Positive
So, C1/m1* c2/m2 is positive
Not Sufficient

b. Y Intercept is calculated when X = 0
C1 * C2 is Negative
Not Sufficient

Together
Since c1*c2 is negative
m1*m2 has to be negative

But, I am confused with how to use the point(4,3)

Kudos [?]: 165 [0], given: 0

Re: xy plane DS   [#permalink] 13 Oct 2008, 16:32
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