If 1 <= a <= 2 and 1 <= b <= 2, what is the least possible value of (a + b)(b - a)? Express your answer as a common fraction.
We know that (a+b)(b-a) simplifies to b^2-a^2 so the least possible value is if b=1 and a=2:
1-4=$\boxed{-3}$
+592 
