What is the end point of the segment MN if N(-1;11) and the midpoint of the segment is (1;5) ?

We have the coordinates of the point N as (-1 , 11). Let the
coordinates of M be (x, y). The mid point of M and N has the coordinates (1,
5)

We know that the mid point of (x1, y1) and (x2, y2) is [(x1 +
x2)/2, (y1 + y2)/2]

So we can write the
equations:

(-1 + x)/2 = 1 and (11 + y)/2 =
5

=> -1 + x = 2 and 11 + y =
10

=> x = 3 and y =
-1

The coordinates of M are (3 ,
-1)