Given the endpoints

Question

Given the endpoint A (4,8) and midpoint M (-3,1), find the missing end point B

Answer 1

If the co-ordinates of the line segment AB are A(a,c) and B(b,d), the co-ordinates of the midpoint M are

M[(a+b)/2,(b+d)/2].

From this information you should be able to solve the problem.

BTW: this is a consequence of the so-called Side Splitter Theorem of plane geometry.