We already have three vertexs: a: (x,y)=(2,3); b:(x,y)= (7,3) and c: (x,y)=(7,-2).
If you see the picture attached, where all points available are in pink, you will see that the distance between the sides that are already defined equals 5.
Because all squares have equals sides, then we must find the missing side that will be at a distance of 5 between the other two vertexs.