Math CentralQuandaries & Queries


Question from Peter, a student:

Segment AB has endpoints A(-1,2) and (3,1). Segment AB is reflected over the y-axis such that A becomes A' and B becomes B'. What is the positive difference between the lengths of segment AA' and segment BB'?

Hi Peter,

The segment AB and its reflection A'B' looks like the following:


Positive difference between the lengths means the same thing as the absolute value of the subtracted lengths. Since |AA'-BB'|=|A'A-BB'|, order does not matter.


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