Question 404397
All three of the points lie on the same line.
The line through (a,b) and (b,a)has slope -1.
The line through(a,b) and (a+1,b-1) has slope -1.
The line through(a,b) and (b+1,a-1) has slope -1.
The point ((a+b)/2,(a+b)/2) is the midpoint of the points (a,b) and (b,a).