Question

Vận dụng các tính chất để tính kết quả theo cách nhanh nhất :

\(1990\times1990-1992\times1998\)

\(\left(1374.57+687.86\right):\left(26.13+74.14\right)\)

 

Answer 1

\(1990\times1990-1992\times1998\)

\(=1990\times1990-\left(1992-2\right)\times\left(1998+2\right)\)

\(=1990\times1990-1990\times1990\)

\(=0\)

Answer 2

\(1990\times1990-1992\times1998\)

\(=1990\times1990-\left(1992-2\right)\times\left(1998+2\right)\)

\(=1990\times1990-1990\times2000\)

\(=3960100-3980000\)

\(=-1990.\)

Answer 3

1990×1990−1992×1998

=1990×1990−(1992−2)×(1998+2)

=1990×1990−1990×\(2000\)

\(=1990\times(1990-2000)\)

\(=1990\times(-10)\)

\(=-19900\)