Ta có :A=98x102 B=100x100
A=98x(100+2) B=100x(98+2)
A=98x100+196 B=100x98+200
Vì 100x98 = 98x100 mà 196 < 200
=> 100x98+196 < 98x100+200
do đó ; A < B
\(A=98.102=\left(100-2\right)\left(100+2\right)=100^2-4< 100^2=B\)
Ta có : A = 98.102 = 98.(100+2) = 9800+98.2
B = 100.100 = 100.(98+2) = 9800+100.2
Vì 9800 = 9800 và 98.2 < 100.2
=> 98.102 < 100.100
=>A < B