Ta có: \(1978\times1979+21\times1980+1958\)

\(=1978\times\left(1978+1\right)+21\times\left(1978+2\right)+1958\)

\(=1978\times1978+1978+21\times1978+42+1958\)

=1978x1978+21x1978+1978+42+1958

=1978x(1978+21)+1978+2000

=1978x1999+3978

=(1979-1)x(1979+20)+3978

=1979x1979+19x1979-20+3978

=1979x1979+19x1979+3958

=1979x(1979+19+2)

=1979x2000

Ta có: 1980x1979-1978x1979

=1979x(1980-1978)=1979x2

Ta có: \(\frac{1978\times1979+21\times1980+1958}{1980\times1979-1978\times1979}\)

\(=\frac{1979\times2000}{1979\times2}=\frac{2000}{2}=1000\)

cọc a ko bik làm :)))

b) 1980 x 1979 - 1978 x 1979 

= ( 1980 - 1978 ) x 1979

= 2 x 1979 

= 3958 

Chúc bạn hok tốt!~~~

b) 1980 . 1979 - 1978 . 1979

= 1979 ( 1980 - 1978 )

=1979 . 2

= 3958

=))

1980*1979-1978*1979

=1979*(1980-1978)

=1979*2

=3957

1980x1979-1978x1979

= 1979x(1980-1978)

= 1979x2

= 3957

1000 đó bạn ơi chuẩn 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000%luôn đó bạn

1000 đó bạn 

nguyễn trung hiếu bấm máy chứ gì 

a ) ( 1978 x 1979 + 1980 x 21 + 1958 ) / ( 1980 x 1979 - 1978 x 1979 ) = 1978 x 1979 + 1980 / 1979 . ( 1980 - 1978 ) 

= 0/1979

a)1000

b) 0

\(\frac{1978\cdot1979+1980\cdot21+1958}{1980\cdot1979-1978\cdot1979}=\frac{1978\cdot1979+\left(1979+1\right)\cdot21+1958}{1979\cdot\left(1980-1978\right)}\)

\(=\frac{1978\cdot1979+1979\cdot21+21+1958}{1979\cdot2}=\frac{1979\cdot\left(1978+21+1\right)}{1979\cdot2}=\frac{2000}{2}=1000\)