Ta có: \(A=1957\cdot1955\)
\(A=\left(1956+1\right)\left(1956-1\right)\)
\(A=1956\cdot1956-1956+1956-1\)
\(A=1956\cdot1956-1\)
\(A=B-1< B\)
Vậy A < B
Ta có : A = 1957 . 1955
B = 1956 . 1956
=> A = 1956 . 1955 + 1955 . 1
<=> B = 1956 . 1955 + 1956 . 1
Vậy A < B