Question

A = 1991x 1999

B = 1995 x 1995

KHÔNG TÍNH HÃY SO SÁNH

Answer 1

Xét hiệu: A-B = \(1991\times1999-1995\times1995=\left(1995-4\right)\left(1995+4\right)-1995\times1995\)

\(=1995\times1995-4\times4-1995\times1995=-4\times4< 0\)

A-B<0 => A<B.

Answer 2

Ta có: A= 1991x1999=1991x(1995+4)=1991x1995+1991x4

          B= 1995x1995=1995x(1991+4)=1991x1995+1995x4

Ta thấy: 1991x1995+1991x4<1991x1995+1995x4

    =>A<B

Vậy A<B