Ta có:
A = -21/10^2016 + -12/10^2017 = -210/10^2017 + -12/10^2017 = -222/10^2017
B = -12/10^2016 + -21/10^2017 = -120/10^2017 + -21/10^2017 = -141/10^2017
Vì: -222/10^2017 < -141/10^2017
⇒ -21/10^2016 + -12/10^2017 < -12/10^2016 + -21/10^2017
⇒ A < B