Question

Tính nhanh:

a) ( 1989 . 1990 + 3978) : ( 1992 . 1991 - 3984 )

Answer 1

$\left(1989.1990+3978\right):\left(1992.1991-3984\right)$

$=\left[1989.\left(1990+2\right)\right]:\left[1992\left(1991-2\right)\right]=\left(1989.1992\right):\left(1992.1989\right)=1$