Question

Segment AB is a segment parallel to the x-axis, where M is the midpoint of segment AB full stop If the length of segment AB equals 20 and the coordinates of M are (−2, 5), what are the coordinates of A?

Answer 1

The x-coordinate differs from -2 by 10, so could be -12 or +8. (The left-right ordering of A and B is not specified here.)
  A = (-12, 5) or (8, 5)

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Whichever one of those is A, B is the other one.