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

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

\(1978\cdot1979+1980\cdot21+\frac{1958}{1980}\cdot1979-1978\cdot1979\)

\(=1980\cdot21+\frac{89}{90}\cdot1979\)

\(=41580+\frac{176131}{90}\)

\(=\frac{3918331}{90}\)

Đề có sai ko mà sao thấy số lớn wá.

nguyễn trung hiếu bấm máy chứ gì 

1980*1979-1978*1979

=1979*(1980-1978)

=1979*2

=3957

1980x1979-1978x1979

= 1979x(1980-1978)

= 1979x2

= 3957

1980*1979-1978*1979

=1979*[1980-1978]

=1979*2

=3958

Đáp án là 1975.210114

xin lỗi do mình tính nhanh thôi

(1978.1979+1980.21+1958)/(1980.1979+1978... 
= (1978.1979+1979.21 + 21 + 1958 )/(1980.1979+1978.1979) 
= (1978.1979+1979.21 + 1979 )/[(1980+1978).1979)] 
= [(1978 + 21+1).1979]/[(1980+1978).1979)] = (2000.1979)/(2.1979.1979) 
= 2000/(2.1979)=1000/1979 

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

= 0/1979

1987 x 1979 + 1980 x 21 + 1958 / 1980 x 1979  - 1978 x 1979

= 1987 x 21 + 1958 / 1979 - 1978

= 41727 + 1958 / 1

= 43685 / 1 = 43685

\(\frac{5521321}{90}\)

a)1000

b) 0