a) Ta có:
A = 123.123 = (124 - 1).(122 + 1) = 124.(122 + 1) - 1.(122 + 1)
= 124.122 + 124 - 123 = 124.122 + 1 `>` 124.122
Vậy A `>` B
b) Ta có:
A = 987.984 = (986 + 1).(985 - 1) = 986.(985 - 1) + 1.(985 - 1)
= 986.985 - 986 + 984
= 986.985 - 2 `<` 986.985
Vậy A `<` B