The line segment joining A(1,3) and B(-2,-1) is extended through each end by a distance equal to it's original length.Find the co-ordinates of the new endpoint.
I don't know what to do.
The coordinates of a vector is the difference of each coordinate of its endpoints :
That should be enough ^^
seeing your other thread, you can also work with midpoints.
A is the midpoint of CB. Find the coordinates of C.
B is the midpoint of BD. Find the coordinates of D.
(draw a sketch if you can't see what I'm talking about )