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# In the xy-plane ,line k passes through the point (1,1) and

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In the xy-plane ,line k passes through the point (1,1) and [#permalink]  11 Jun 2010, 06:24
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In the xy-plane, line k passes through the point (1,1) and line m passes through the point (1,-1). Are the lines k and m perpendicular to each other

(1) Lines k and m intersect at the point (1,-1)
(2) Line k intersects the x axis at the point (1,0)
[Reveal] Spoiler: OA
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Re: Help needed on intersecting lines in coordinate geometry [#permalink]  11 Jun 2010, 06:33
IMO E.

S1) If line k passes thru (1, 1) and (1, -1) then it is parallel to y axis but we dont know one more different point for line m. Insufficient.

S2) Similar to S1.

S1+S2: Similar to S1, Insufficient.

So, E.
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Re: Help needed on intersecting lines in coordinate geometry [#permalink]  11 Jun 2010, 07:01
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gautamsubrahmanyam wrote:
In the xy-plane ,line k passes through the point (1,1) and line m passes through the point (1,-1).Are the lines k and m perpendicular to each other

(1) Lines k and m intersect at the point (1,-1)
(2) Line k intersects the x axis at the point (1,0)

For one line to be perpendicular to another, their slopes must be negative reciprocals of each other (if slope of one line is $$m$$ than the slope of the line perpendicular to this line is $$-\frac{1}{m}$$). In other words, the two lines are perpendicular if and only the product of their slopes is $$-1$$.

So basically the question is can we somehow calculate the slopes of these lines.

From stem we have one point for each line.

(1) gives us the second point of line $$k$$, hence we can get the slope of this line, but we still know only one point of line $$m$$. Not sufficient.

(2) again gives the second point of line $$k$$, hence we can get the slope of this line, but we still know only one point of line $$m$$. Not sufficient.

(1)+(2) we can derive the slope of line $$k$$ but for line $$m$$ we still have only one point, hence we can not calculate its slope. Not sufficient.

For more on this issue please check Coordinate Geometry chapter of Math Book (link in my signature).

ALSO:
 ! Please post PS questions in the PS subforum: gmat-problem-solving-ps-140/Please post DS questions in the DS subforum: gmat-data-sufficiency-ds-141/No posting of PS/DS questions is allowed in the main Math forum.

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GMAT PREP DS [#permalink]  22 Aug 2010, 17:48
Hey everyone,

Thanks to everyone that responded to my previous round of posts, it was extremely helpful! I have some more questions that I need help with. Here it goes:

In the xy-plane, line k passes through the point (1,1) and line m passes through the point (1,-1). Are lines ka nd m perpendicular to each other?

(1) Lines k and m intersect at the point (1, -1)
(2) Line k intersects the x-axis at the point (1,0)
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Re: GMAT PREP DS [#permalink]  22 Aug 2010, 17:53
1. k goes through 1,1 and 1,-1, m can be anyslope. not suff
2. k intersects xaxis at 1,0 <- this probably can be seen from (1) itself. no info about m. not suff
1+2 -> m can be anything. can't say, E
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Re: GMAT PREP DS [#permalink]  22 Aug 2010, 18:24
Thanks for the post but I'm still not grasping the concept. When two lines intersect, doesn't that mean that they are perpendicular to each other?
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Re: GMAT PREP DS [#permalink]  22 Aug 2010, 18:54
uzzy12 wrote:
Thanks for the post but I'm still not grasping the concept. When two lines intersect, doesn't that mean that they are perpendicular to each other?

Yes, when two lines intersect, their angle may or may not be 90 degree. Also we need to find the slope of the two lines (m1 and m2) and for the two lines to be perpendicular, m1 * m2 should be equal to -1.

Since the slope could not be uniquely identified, we cannot conclude that they are perpendicular.
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Re: GMAT PREP DS [#permalink]  22 Aug 2010, 19:01
uzzy12 wrote:
Thanks for the post but I'm still not grasping the concept. When two lines intersect, doesn't that mean that they are perpendicular to each other?

No when 2 lines intersect they are not necessarily perpedicular to each other. They could intersect at many angles...
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Re: Help needed on intersecting lines in coordinate geometry [#permalink]  16 May 2012, 07:05
I did not understand why you said you can find out only line K slope from statement 1 - why not m

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Re: Help needed on intersecting lines in coordinate geometry [#permalink]  16 May 2012, 08:17
Expert's post
venmic wrote:
I did not understand why you said you can find out only line K slope from statement 1 - why not m

Even when considering the statements together we still know only one point of line m: (1, -1). We cannot get the slope based on just one point of a line.

For more check Coordinate Geometry chapter of Math Book: math-coordinate-geometry-87652.html

Hope it helps.
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In the XY plane.. [#permalink]  06 Jun 2012, 22:06
In the xy-plane, line passes through the point (1,1) and line m passes through the point (1,-1). Are lines k and m perpendicular?

1) Lines k and m intersect at the point (1,-1)
2) Line k intersects the x-axis at the point (1,0)
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Re: In the XY plane.. [#permalink]  06 Jun 2012, 22:36
From statement-1, we can say that line K is X=1. But line M can be any line passing through (1,-1). So, Statement-1 is not sufficient.

From statement-2 also, line K is X=1. But line M can be any line through (1,-1). So, even statement 2 is not sufficient.

Though we combine both the statements, no additional information can be obtained about line M. Hence, E.
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Re: In the XY plane.. [#permalink]  07 Jun 2012, 15:36
Could you tell me how to determine whether the lines are perpendicular just in general??
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Re: In the XY plane.. [#permalink]  07 Jun 2012, 15:46
Expert's post
Val1986 wrote:
In the xy-plane, line passes through the point (1,1) and line m passes through the point (1,-1). Are lines k and m perpendicular?

1) Lines k and m intersect at the point (1,-1)
2) Line k intersects the x-axis at the point (1,0)

Merging similar topics.

Val1986 wrote:
Could you tell me how to determine whether the lines are perpendicular just in general??

For one line to be perpendicular to another, their slopes must be negative reciprocals of each other (if slope of one line is $$m$$ than the slope of the line perpendicular to this line is $$-\frac{1}{m}$$). In other words, the two lines are perpendicular if and only the product of their slopes is $$-1$$.

For more check Coordinate Geometry chapter of Math Book: math-coordinate-geometry-87652.html

Hope it helps.
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Re: In the xy-plane ,line k passes through the point (1,1) and [#permalink]  20 Dec 2013, 11:32
gautamsubrahmanyam wrote:
In the xy-plane, line k passes through the point (1,1) and line m passes through the point (1,-1). Are the lines k and m perpendicular to each other

(1) Lines k and m intersect at the point (1,-1)
(2) Line k intersects the x axis at the point (1,0)

They don't mention that they have to be different lines do they? Can it be the same vertical line as well?

Thanks
Cheers!
J
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Re: In the xy-plane ,line k passes through the point (1,1) and [#permalink]  21 Dec 2013, 04:47
Expert's post
jlgdr wrote:
gautamsubrahmanyam wrote:
In the xy-plane, line k passes through the point (1,1) and line m passes through the point (1,-1). Are the lines k and m perpendicular to each other

(1) Lines k and m intersect at the point (1,-1)
(2) Line k intersects the x axis at the point (1,0)

They don't mention that they have to be different lines do they? Can it be the same vertical line as well?

Thanks
Cheers!
J

Yes, nothing in the question prevents m and k to be the same line.
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Re: In the xy-plane ,line k passes through the point (1,1) and   [#permalink] 21 Dec 2013, 04:47
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