Coordiante plane- How to arrive at the answer?

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Divya Ann Chacko: Senior | Next Rank: 100 Posts; Posts: 42; Joined: Mon Nov 25, 2013 8:30 am

by Divya Ann Chacko » Tue Dec 17, 2013 8:20 pm

In the xy coordinate plane, is point R equidistant from points (-3,-3) and (1,-3)?
1) The x coordiante of point R is -1
2) Point R lies on the line y=-3

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Source: Beat The GMAT — Data Sufficiency | Tue Dec 17, 2013 8:20 pm

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Coordiante plane- How to arrive at the answer?

by Brent@GMATPrepNow » Tue Dec 17, 2013 8:31 pm

Divya Ann Chacko wrote:In the xy coordinate plane, is point R equidistant from points (-3,-3) and (1,-3)?
1) The x coordiante of point R is -1
2) Point R lies on the line y=-3

Target question: Is point R equidistant from points (-3,-3) and (1,-3)?

This question is a great candidate for rephrasing the target question.
Aside: We have a free video with tips on rephrasing the target question: https://www.gmatprepnow.com/module/gmat- ... cy?id=1100

First sketch the two given points

Notice that the point (-1, -3) is equidistant from the two given points. MORE IMPORTANTLY, every point on the line x = -1 is equidistant from the two given points.

So, we can rephrase the target question . . .
Rephrased target question: Is point R on the line x = -1?

Statement 1: The x coordinate of point R is -1
If the x-coordinate is -1, then point R is definitely on the line x = -1
Since we can answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: Point R lies on the line y= -3
This tells us nothing about whether or not point R is on the line x = -1?
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Answer = A

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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Emi-Beth: Newbie | Next Rank: 10 Posts; Posts: 5; Joined: Tue Jul 05, 2011 3:29 am

by Emi-Beth » Sun Jul 30, 2017 1:30 pm

I do not understand this answer. How can every point on the line x = -1 be equidistant from the given points? For example (-1,3) is not equidistant to the given points. Seems to me the only correct answer is (-1, -3). Please explain further why EVERY POINT ON THE LINE X=-1 IS EQUIDISTANT to the given points. I would understand this if we were plotting a straight line rather than points.

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GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Sun Jul 30, 2017 2:31 pm

Emi-Beth wrote:I do not understand this answer. How can every point on the line x = -1 be equidistant from the given points? For example (-1,3) is not equidistant to the given points. Seems to me the only correct answer is (-1, -3). Please explain further why EVERY POINT ON THE LINE X=-1 IS EQUIDISTANT to the given points. I would understand this if we were plotting a straight line rather than points.

The SYMMETRY exhibited by the dashed blue line segments in the figure above illustrate why every point on x=-1 is equidistant from (-3, -3) and (1, -3).

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Emi-Beth: Newbie | Next Rank: 10 Posts; Posts: 5; Joined: Tue Jul 05, 2011 3:29 am

by Emi-Beth » Mon Jul 31, 2017 1:12 pm

Brilliant. Thank you. I understand now. my challenge was visualizing "equidistant" and your illustration shows this perfectly.

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