\(C=\dfrac{4}{9}\times\dfrac{13}{17}+\dfrac{4}{17}\times\dfrac{4}{9}+\dfrac{2}{9}\\ =\dfrac{4}{9}\times\left(\dfrac{13}{17}+\dfrac{4}{17}\right)+\dfrac{2}{9}\\ =\dfrac{4}{9}\times1+\dfrac{2}{9}\\ =\dfrac{4}{9}+\dfrac{2}{9}\\ =\dfrac{6}{9}=\dfrac{2}{3}\)

\(D=\dfrac{8}{19}\times\dfrac{5}{11}+\dfrac{7}{11}\times\dfrac{8}{19}+\dfrac{12}{11}\times\dfrac{11}{19}\\ =\dfrac{8}{19}\times\left(\dfrac{5}{11}+\dfrac{7}{11}\right)+\dfrac{12}{11}\times\dfrac{11}{19}\\ =\dfrac{8}{19}\times\dfrac{12}{11}+\dfrac{12}{11}\times\dfrac{11}{19}\\ =\dfrac{12}{11}\times\left(\dfrac{8}{19}+\dfrac{11}{19}\right)\\ =\dfrac{12}{11}\times19\\ =\dfrac{12}{11}\)

\(C=\dfrac{4}{9}\cdot\dfrac{13}{17}+\dfrac{4}{17}\cdot\dfrac{4}{9}+\dfrac{2}{9}\)

\(C=\dfrac{4}{9}\cdot\left(\dfrac{13}{17}+\dfrac{4}{17}\right)+\dfrac{2}{9}\)

\(C=\dfrac{4}{9}\cdot\dfrac{13+4}{17}+\dfrac{2}{9}\)

\(C=\dfrac{4}{9}\cdot\dfrac{17}{17}+\dfrac{9}{2}\)

\(C=\dfrac{4}{9}\cdot1+\dfrac{2}{9}\)

\(C=\dfrac{4}{9}+\dfrac{2}{9}\)

\(C=\dfrac{4+2}{9}\)

\(C=\dfrac{6}{9}\)

\(C=\dfrac{2}{3}\)

\(D=\dfrac{8}{19}\cdot\dfrac{5}{11}+\dfrac{7}{11}\cdot\dfrac{8}{19}+\dfrac{12}{11}\cdot\dfrac{11}{19}\)

\(D=\dfrac{8}{19}\cdot\left(\dfrac{5}{11}+\dfrac{7}{11}\right)+\dfrac{12}{11}\cdot\dfrac{11}{19}\)

\(D=\dfrac{8}{19}\cdot\dfrac{12}{11}+\dfrac{12}{11}\cdot\dfrac{11}{19}\)

\(D=\dfrac{12}{11}\cdot\left(\dfrac{8}{19}+\dfrac{11}{19}\right)\)

\(D=\dfrac{12}{11}\cdot\dfrac{19}{19}\)

\(D=\dfrac{12}{11}\cdot1\)

\(D=\dfrac{12}{11}\)

\(a,-\dfrac{3}{5}.y=\dfrac{21}{10}\)

\(y=\dfrac{21}{10}:\dfrac{-3}{5}=\dfrac{-7}{2}\)

\(b,y:\dfrac{3}{8}=-1\dfrac{31}{33}\)

\(y=-1\dfrac{31}{33}.\dfrac{3}{8}=\dfrac{-8}{11}\)

Vậy \(y=-\dfrac{8}{11}\)

\(c,1\dfrac{2}{5}.y+\dfrac{3}{7}=-\dfrac{4}{5}\)

\(\Rightarrow1\dfrac{2}{5}y=-\dfrac{4}{5}-\dfrac{3}{7}=\dfrac{-43}{35}\)

\(\Rightarrow y=\dfrac{-43}{35}:1\dfrac{2}{5}=\dfrac{-43}{49}\)

\(d,-\dfrac{11}{12}.y+0,25=\dfrac{5}{6}\)

\(\Rightarrow-\dfrac{11}{12}.y=\dfrac{5}{6}-0,25=\dfrac{7}{12}\)

\(\Rightarrow y=\dfrac{7}{12}:\dfrac{-11}{12}=\dfrac{-7}{11}\)

C)

`7/19xx5/8xx (-19)/7`

`=7/19xx (-19/7)xx5/8`

`= -1xx5/8`

`=-5/8`

D)

`3/7xx9/11+3/7xx2/11`

`=3/7xx(9/11+2/11)`

`=3/7xx11/11`

`=3/7xx1`

`=3/7`

\(A=\dfrac{-19}{9}.\dfrac{1}{2}-\dfrac{4}{11}.\dfrac{-11}{9}+\left(-\dfrac{2}{3}\right)=-\dfrac{23}{18}\)

\(B=\left(-\dfrac{15}{6}\right):\dfrac{-1}{2}+\dfrac{7}{-12}-\dfrac{1}{3}.\dfrac{-11}{2}=\dfrac{25}{4}\)

\(C=\dfrac{3}{4}.\left(-8\right)-\dfrac{1}{3}.\dfrac{-7}{2}-\dfrac{5}{18}=-\dfrac{46}{9}\)

\(A=\dfrac{-19}{18}+\dfrac{4}{9}-\dfrac{2}{3}=\dfrac{-19}{18}+\dfrac{8}{18}-\dfrac{12}{18}=\dfrac{-23}{18}\)

\(B=\dfrac{-5}{2}\cdot\dfrac{-2}{1}-\dfrac{7}{12}+\dfrac{11}{6}=\dfrac{5\cdot12-7+22}{12}=\dfrac{75}{12}=\dfrac{25}{4}\)

a) \(3\times\dfrac{4}{11}=\dfrac{3\times4}{11}=\dfrac{12}{11}\)

b) \(1\times\dfrac{5}{4}=\dfrac{1\times5}{4}=\dfrac{5}{4}\)

c) \(0\times\dfrac{2}{5}=\dfrac{0\times2}{5}=\dfrac{0}{5}=0\)

a: \(=\dfrac{3\cdot4}{11}=\dfrac{12}{11}\)

b: \(=\dfrac{1\cdot5}{4}=\dfrac{5}{4}\)

c: \(=\dfrac{0\cdot2}{5}=0\)

a) 683\(\times\) 35=23906

    1954\(\times\) 425=830450

    2438\(\times\) 306=746028

b) \(\dfrac{7}{9}\times\dfrac{3}{35}=\dfrac{7\times3}{9\times35}=\dfrac{1}{15}\) 

\(\dfrac{9}{22}\times55=\dfrac{9\times55}{22}=\dfrac{45}{2}\) 

\(\dfrac{11}{17}:\dfrac{33}{34}=\dfrac{11}{17}\times\dfrac{34}{33}=\dfrac{11\times34}{17\times33}=\dfrac{2}{3}\) 

c) 36,66:7,8=4,7

     15,7:6,28=2,5

      27,63:0,45=61,4

d) 16 giờ 15 phút:5=3 giờ 15 phút

    14 phút 36 giây:12=1 phút 13 giây

a: \(\Leftrightarrow\left(x-1\right)^2=81\)

\(\Leftrightarrow\left[{}\begin{matrix}x-1=9\\x-1=-9\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=10\\x=-8\end{matrix}\right.\)

a) $\frac{7}{2} \times \frac{1}{6} = \frac{7}{{12}}$

b) $\frac{8}{{11}} \times 4 = \frac{{32}}{{11}}$

c) $\frac{8}{9}:\frac{2}{5} = \frac{8}{9} \times \frac{5}{2} = \frac{{40}}{{18}} = \frac{{20}}{9}$

d) $\frac{5}{8}:7 = \frac{5}{8} \times \frac{1}{7} = \frac{5}{{56}}$

`5 / 9 xx 7 / 13 + 5 / 9 xx 8 / 13 - 5 / 13 xx 2 / 9`

`=5 / 9 xx 7 / 13 + 5 / 9 xx 8 / 13 - 5 / 9 xx 2 / 13`

`= 5 / 9 xx ( 7 / 13 + 8 / 13 - 2 / 13 )`

`= 5 / 9 xx 13 / 13 = 5 / 9`

hông pé ơi ah ko bày đâu

$\frac{5}{9}\times \frac{7}{13}+\frac{5}{9}\times \frac{8}{13}-\frac{5}{13}\times \frac{2}{9}$

$=\frac{5}{9}\times \frac{7}{13}+\frac{5}{9}\times \frac{8}{13}-\frac{5}{9}\times \frac{2}{13}$

$=\frac{5}{9}\times (\frac{7}{13}+\frac{8}{13}-\frac{2}{13})$

$=\frac{5}{9}\times \frac{13}{13}=\frac{5}{9}$

a) \(\dfrac{3}{5}+\dfrac{7}{25}=\dfrac{15}{25}+\dfrac{7}{25}=\dfrac{15+7}{25}=\dfrac{22}{25}\)

b) \(\dfrac{8}{11}-\dfrac{19}{33}=\dfrac{24}{33}-\dfrac{19}{33}=\dfrac{24-19}{33}=\dfrac{5}{33}\)

c) \(\dfrac{16}{21}\times\dfrac{3}{5}=\dfrac{16\times3}{21\times5}=\dfrac{48}{105}=\dfrac{16}{35}\)

d) \(\dfrac{14}{41}\div\dfrac{7}{9}=\dfrac{14}{41}\times\dfrac{9}{7}=\dfrac{14\times9}{41\times7}=\dfrac{126}{287}=\dfrac{18}{41}\)