Question

A line segment has (x1, y1) as one endpoint and (xm, ym) as its midpoint. Find the other endpoint (x2, y2) of the line segment in terms of x1, y1, xm, and ym.

Answer 1

Midpoint (xm, ym) = ((x1 + x2)/2, (y1 + y2)/2)
xm = (x1 + x2)/2
2xm = x1 + x2
x2 = 2xm - x1
y2 = 2ym - y1

Therefore, (x2, y2) = (2xm - x1, 2ym - y1)