Let m be the difference of x-coordinates and n, that of y-ones.
[tex]m=|-6-4|=10 \\
n=|8-4|=4[/tex]
Now, we have two ways to find the other endpoint, since these differences are the same to those between the missing endpoint's coordinates and the midpoint's ones, and twice m and n are the differences between the known endpoint and the one we're looking for.
So, solving this problem by the first way just cited:
The other endpoint is:
[tex](4+m,\,8+n)=(4+10,\,8+4)=(14,\,12)[/tex]
