Our goal here is to create a copy of line segment PQ, through various steps. Let's start with drawing line segment PQ, respectively point R a fixed distance away from the segment.
It would be wise to use a compass in this case, and a ruler for certain.
So we have this segment PQ, and point R a " fixed distance " away from PQ.
( 1. Extend a compass to match with the length of PQ,
( 2. Move this compass ( without changing it's length ) so that one endpoint matches with point R
( 3. Now draw an arc with this compass, where this line will be
( 4. Take your ruler and draw a straight line from this point R to your arc. It would be wise to draw this line to the middle of the arc you created.
If you like, take a look at the attachment below to see what it should look like.
I have done these questions before, so I can assure you that this experiment is proved correctly!