\(=\left(1999\times1998+1998\times1997\right)\times\left(1+\dfrac{1}{2}:1\dfrac{1}{2}-1\dfrac{1}{3}\right)\)

\(=\left(1999\times1998+1998\times1997\right)\times\left(1+\dfrac{1}{2}:\dfrac{3}{2}-\dfrac{4}{3}\right)\)

\(=\left(1999\times1998+1998\times1997\right)\times\left(1+\dfrac{1}{3}-\dfrac{4}{3}\right)\)

\(=\left(1999\times1998+1998\times1997\right)\times\left(\dfrac{4}{3}-\dfrac{4}{3}\right)\)

\(=\left(1999\times1998+1998\times1997\right)\times0\)

\(=0\)

1998 x 497 +1998 x 1 + 1998 x 1 + 1998 x1

= 1998 x (497+1+1+1)

=1998 x500 = 999000

1998x497+1998+1998+1998

= 1998 x 497 + 1998 x 3

= 1998 x (497+3)

= 1998 x 500

= 999000

1998x497+1998+1998+1998

=1998x497+1998x3

=1998x(497+3)

=1998x500

=999000

HỌC TỐT NHÉ!

1998^2-1997(1998+1)

=1998^2-(1998-1)(1998+1)

=1998^2-(1998^2-1)

=1998^2-1998^2+1

=1

1/1998 x ( 6/7 + 4/7 - 6/14 )

= 1/1998 x 1

= 1/1998

1/1998 x 6/7 + 1/1998 x 4/7 - 1/1998 x 6/14=1/1998x(6/7+4/7-6/14)=1/1998x(12/14+8/14-6/14)=1/1998x2=2/1998=1/999

=1998.1998-1996.(1998+2)

=1998.1998-1996.1998+1996.2

=1998.(1998-1996)+1996.2

=1998.2+1996.2

=2.(1998+1996)

=2.3994

=7988

1998.1998-1996.2000=4

1998x1998-1996x2000=(1996+2)x1998-1996x(1998+2)=1996x1998+2x1998-1996x1998+1996x2=2x1998-1998x2=2x(1998-1996)=2x2=4

Tick nhé Tạ_Thu_Hiền

câu thứ nhất bằng 7876638900

câu thứ 2 bằng 798081399759

1990.1990-1992.1988

=1990.(1988+2)-(1990+2).1988

=1990.1988+1990.2-1990.1988+1988.2

= (1990-1988).2

=2.2

=4