To do the first part I would imagine you need to show that the distance between and is 1/3 the distance between and .

So the distance between and is:

Note that is the distance between and so we have proven what we have set out to show.

For the second part we need to find the midpoint of the two points and .

This is your second point of trisection.

I'll do a) as an example. We are given the points (1 , -2) and (4, -1). The first point of trisection is:

The second point of trisection is:

-Dan