Given the endpoint (2,-3) and the misdpoint (1,0.5), explain how to determine the other endpoint?

The given midpoint lies on the segment whose endpoints
are  P(2,-3) and N(xN,yN).

For finding the coordinates of
the midpoint M(xM, yM), we have to solve the
system:

xN=2xM-xP, where xM=1 and
xP=2

yN=2yM-yP, where yM=1/2 and
yP=-3

Now, we just have to substitute the known
values:

xN=2*1-2

xN=0

yN=2*(1/2)-(-3)

yN
= 1 + 3

yN=4

The
coordinates of the other endpoint of the segment whose midpoint is (1 , 1/2) are:
(0,4).