If there are n tiles along the entire edge of a square room, then let x be the number of tiles along one width of the room. Thus there must be x-2 tiles along one length of the room (We can't count a tile twice; draw a picture to help visualize this).
Thus we can obtain an expression for n:
Solving for x in terms of n:
Since x denotes the number of tiles along the width of the room, and the room is a square, the total number of tiles is . Hence
Since the smallest square room possible for n tiles along the edge is n = 4 (a 2x2 tile room), then the domain of is all .