\(a)\)\(\left(1989.1990+3978\right)\div\left(1992.1991-3984\right)\)

\(=\)\(\left(1989.1990+1989.2\right)\div\left(1992.1991-1992.2\right)\)

\(=\)\(\left[1989.\left(1990+2\right)\right]\div\left[1992.\left(1991-2\right)\right]\)

\(=\)\(\left(1989.1991\right)\div\left(1992.1989\right)\)

\(=\)\(1\)

\(b)\)\(\left(637.527-189\right)\div\left(526.637+448\right)\)

\(=\)\(\left[637.\left(526-1\right)-189\right]\div\left(526.637-448\right)\)

\(=\)\(\left[637.526+\left(637-198\right)\right]\div\left(637.526-448\right)\)

\(=\)\(\left(636.526+448\right)\div\left(637.526-448\right)\)

\(=\)\(1\)

Rút gọn phân số:\(\frac{1989.1990+3978}{1992.1991-3984}\)

\(=\frac{1989.1990+1989.2}{1992.1991-1992.2}=\frac{1989.\left(1990+2\right)}{1992.\left(1991-2\right)}=\frac{1989.1992}{1992.1989}=1\)

học giỏi nha

\(\frac{1989\cdot1990+3978}{1992\cdot1991-3984}\)

\(=\frac{1989\cdot1990+1989\cdot2}{1992\cdot1991-1992\cdot2}\)

\(=\frac{1989\cdot\left(1990+2\right)}{1992\cdot\left(1991-2\right)}\)

\(=\frac{1989\cdot1992}{1992\cdot1989}=1\)

cảm ơn

1989.1990+3978 / 1992.1991-3984 = 1989.1990+1989x2 / 1992.1991-1992x2
 = 1989.(1990=2) / 1992.(1991-2) = 1989.1992 / 1992.1989 = 1

176/187=?

1989.1990+3978/1992.1991-3984

=1989.1990+1989.2/1992.1991-1992.2

=1989.(1990+2)/1992.(1991-2)

=1989.1992/1992.1989

\(\dfrac{1989.1990+3978}{1992.1991+3984}\)
= \(\dfrac{1989.1990+2.1989}{1992.1991+2.1992}\)
=\(\dfrac{1989.\left(1990+2\right)}{1992.\left(1991+2\right)}\)
=\(\dfrac{1989.1992}{1992.1992}\)
=\(\dfrac{1989}{1993}\).

a) \(A=\dfrac{6.9-2.17}{63.3-119}=\dfrac{2.3.9-2.17}{7.9.3-7.17}=\dfrac{2.27-2.17}{7.27-2.17}=\dfrac{2\left(27-17\right)}{7\left(27-17\right)}=\dfrac{2.10}{7.10}=\dfrac{2}{7}\)

b)\(B=\dfrac{1989.1990+3978}{1992.1991-3984}=\dfrac{1989.1990+2.1989}{1992.1991-2.1992}=\dfrac{1989.\left(1990+2\right)}{1992.\left(1991-2\right)}=\dfrac{1989.1992}{1992.1989}=1\)

\(\dfrac{13.11-13}{13.15}=\dfrac{13.11-13.1}{13.15}=\dfrac{13.\left(11-1\right)}{13.15}=\dfrac{13.10}{13.15}=\dfrac{1.2}{1.3}=\dfrac{2}{3}\)

\(\dfrac{1989.1990+3978}{1992.1991-3984}=\dfrac{1989.1990+2.1989}{1992.1991-2.1992}=\dfrac{1989.\left(1990+2\right)}{1992.\left(1991-2\right)}=\dfrac{1989.1992}{1992.1989}=\dfrac{1.1}{1.1}=1\)

Lời giải:

a, \(\dfrac{13.11-13}{13.15}=\dfrac{13.\left(11-1\right)}{13.15}=\dfrac{13.10}{13.15}=\dfrac{2}{3}\)

b, \(\dfrac{1989.1990+3978}{1992.1991-3984}=\dfrac{1989.1990+1989.2}{1992.1991-1992.2}=\dfrac{1989.\left(1990+2\right)}{1992.\left(1991-2\right)}=\dfrac{1989.1992}{1992.1989}=1\)

Tham khảo link này nha

https://olm.vn/hoi-dap/detail/99130422647.html

Ta có :

1989.1990+3978=1989.1990+1989.2=1989.1992

1992.1991-3984=1992.1991-1992.2=1992.1989

Gộp cả 2 cái ta có :

1989 . 1992 / 1992 . 1989 = 1

Nguồn học247

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