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In the xy-plane , line l intersects a circle with center

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In the xy-plane , line l intersects a circle with center [#permalink] New post 19 Aug 2013, 10:16
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Question Stats:

42% (02:04) correct 58% (01:11) wrong based on 66 sessions
In the xy-plane, line l intersects a circle with center at origin. Is the slope of line l equal to zero?

(1) Line l passes through second quadrant.

(2) Line l is perpendicular to the tangent of the circle.
[Reveal] Spoiler: OA

Last edited by Bunuel on 17 Jul 2014, 10:58, edited 1 time in total.
Edited the OA.
1 KUDOS received
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Re: In the xy-plane , line l intersects a circle with center [#permalink] New post 19 Aug 2013, 11:04
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innocous wrote:
In the xy-plane , line l intersects a circle with center at origin.Is the slope of line l equal to zero?

1) line l passes through second quadrant.

2) line l is perpendicular to the tangent of the circle.


ALL LINES WHICH ARE PERPENDICULAR TO TANGENT WILL PASS THROUGH CENTRE.

IMO C.

SEE DIAG FOR EXPLANATION.
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Re: In the xy-plane , line l intersects a circle with center [#permalink] New post 22 Aug 2013, 03:47
In the xy-plane , line l intersects a circle with center at origin.Is the slope of line l equal to zero?

1) line l passes through second quadrant.
2) line l is perpendicular to the tangent of the circle.

FS1: Line l passing through second quadrant and intersecting the circle can be either parall to x-axis(in which case its slope is 0) or not parallel to x-axis(slope not eual to 0). Hence insufficient.
FS2: Line which is perpendicular to the tangent must pass thought centre (since angle betwwen radius and point of contact of tangent to a circle is 90 degrees). Hence, the line can have multiple possibilities for its slope (including 0 and infinity when the line is parallel to x or y axis respectively). Not sufficient.

Combining the above two, the only possibility is when the slope is negatice but not zero (x-axis is not in II quadrant). Hence slope iof line l is not zero for any case.
Sufficient. So answer should be C.
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Re: In the xy-plane , line l intersects a circle with center [#permalink] New post 17 Jul 2014, 10:15
zerosleep wrote:
In the xy-plane , line l intersects a circle with center at origin.Is the slope of line l equal to zero?

1) line l passes through second quadrant.
2) line l is perpendicular to the tangent of the circle.

FS1: Line l passing through second quadrant and intersecting the circle can be either parall to x-axis(in which case its slope is 0) or not parallel to x-axis(slope not eual to 0). Hence insufficient.
FS2: Line which is perpendicular to the tangent must pass thought centre (since angle betwwen radius and point of contact of tangent to a circle is 90 degrees). Hence, the line can have multiple possibilities for its slope (including 0 and infinity when the line is parallel to x or y axis respectively). Not sufficient.

Combining the above two, the only possibility is when the slope is negatice but not zero (x-axis is not in II quadrant). Hence slope iof line l is not zero for any case.
Sufficient. So answer should be C.



The 2nd statement does not imply that the line l has to pass through the tangent point. It could be any parallel line perpendicular to the tangent.
Shouldn't the answer be E?

Please clarify??
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Re: In the xy-plane , line l intersects a circle with center [#permalink] New post 17 Jul 2014, 10:57
Expert's post
faamir wrote:
zerosleep wrote:
In the xy-plane , line l intersects a circle with center at origin.Is the slope of line l equal to zero?

1) line l passes through second quadrant.
2) line l is perpendicular to the tangent of the circle.

FS1: Line l passing through second quadrant and intersecting the circle can be either parall to x-axis(in which case its slope is 0) or not parallel to x-axis(slope not eual to 0). Hence insufficient.
FS2: Line which is perpendicular to the tangent must pass thought centre (since angle betwwen radius and point of contact of tangent to a circle is 90 degrees). Hence, the line can have multiple possibilities for its slope (including 0 and infinity when the line is parallel to x or y axis respectively). Not sufficient.

Combining the above two, the only possibility is when the slope is negatice but not zero (x-axis is not in II quadrant). Hence slope iof line l is not zero for any case.
Sufficient. So answer should be C.



The 2nd statement does not imply that the line l has to pass through the tangent point. It could be any parallel line perpendicular to the tangent.
Shouldn't the answer be E?

Please clarify??


You are right the answer must be E:
Attachment:
Untitled.png
Untitled.png [ 26.48 KiB | Viewed 231 times ]

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Re: In the xy-plane , line l intersects a circle with center [#permalink] New post 17 Jul 2014, 11:04
Bunuel,

Thank you so much for the quick response. You are the best :D
Re: In the xy-plane , line l intersects a circle with center   [#permalink] 17 Jul 2014, 11:04
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