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Another coordinates question?

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Source: — Problem Solving |

by ganeshrkamath » Sun Aug 25, 2013 8:28 am
yumi2012 wrote:The line represented by equation y=x is the perpendicular bisector of line segment AB. If A has the coordinates (-3,3), what are the coordinates of B?
y=x
A perpendicular line will have a slope of -1.
y=-x
Image
The figure clearly shows the coordinates of point B as [spoiler](3,-3)[/spoiler].

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by Brent@GMATPrepNow » Sun Aug 25, 2013 9:54 am
Saying that line represented by equation y=x is the perpendicular bisector of line segment AB, is a fancy way of saying that point B is a mirror reflection of point A across the line y=x (in other words, the mirror is the line y=x).

This is probably beyond the scope of the GMAT, but if some point (a,b) is reflected across the line y=x, the reflected point is (b,a)

So, for example, if the point (9,2) is reflected across the line y=x, the reflected point is (2,9)

The question basically tells us that the point (-3, 3) is reflected across the line y=x, so the reflected point (point B) is at [spoiler](3, -3) [/spoiler]

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