1) Ta có: \(\left(\dfrac{3}{4}\cdot\dfrac{5}{97}+\dfrac{1}{9}\cdot\dfrac{13}{47}\right)\cdot\left(\dfrac{1}{5}-\dfrac{7}{25}\cdot\dfrac{5}{7}\right)\)

\(=\left(\dfrac{3}{4}\cdot\dfrac{5}{97}+\dfrac{1}{9}\cdot\dfrac{13}{47}\right)\cdot\left(\dfrac{1}{5}-\dfrac{1}{5}\right)\)

=0

2) Ta có: \(\dfrac{8}{17}\cdot\dfrac{4}{15}+\dfrac{8}{17}\cdot\dfrac{22}{15}-\dfrac{8}{15}\cdot\dfrac{9}{17}\)

\(=\dfrac{8}{17}\left(\dfrac{4}{15}+\dfrac{22}{15}-\dfrac{9}{15}\right)\)

\(=\dfrac{8}{17}\cdot\dfrac{15}{15}=\dfrac{8}{17}\)

3) Ta có: \(\dfrac{2021}{2}\cdot\dfrac{1}{3}+\dfrac{4042}{4}\cdot\dfrac{1}{5}+\dfrac{6063}{3}\cdot\dfrac{22}{15}\)

\(=\dfrac{2021}{2}\left(\dfrac{1}{3}+\dfrac{1}{5}\right)+2021\cdot\dfrac{22}{15}\)

\(=\dfrac{2021}{2}\cdot\dfrac{8}{15}+\dfrac{2021}{2}\cdot\dfrac{44}{15}\)

\(=\dfrac{2021}{2}\cdot\dfrac{52}{15}\)

\(=\dfrac{52546}{15}\)

4) Ta có: \(\dfrac{4}{7}\cdot\dfrac{2}{13}+\dfrac{8}{13}:\dfrac{7}{4}+\dfrac{4}{7}:\dfrac{13}{2}+\dfrac{4}{7}\cdot\dfrac{1}{13}\)

\(=\dfrac{4}{7}\left(\dfrac{2}{13}+\dfrac{8}{13}+\dfrac{2}{13}+\dfrac{1}{13}\right)\)

\(=\dfrac{4}{7}\)

1) Tính biểu thức:

a) Thiếu đề

b) ` 4/7 xx 8/13 + 8/13 xx 3/7`

= ` 8/13 xx ( 4/7 + 3/7)`

` = 8/13 xx 7/7`

` = 8/13 xx 1`

` = 8/13`

a) thiếu đề

b) \(=\left(\dfrac{4}{7}+\dfrac{3}{7}\right)\times\dfrac{8}{13}\\ =1\times\dfrac{8}{13}=\dfrac{8}{13}\)

2: \(=\dfrac{-2}{75}+\dfrac{5}{39}=\dfrac{33}{325}\)

3: \(=\dfrac{6}{11}\left(\dfrac{4}{9}+\dfrac{5}{9}\right)=\dfrac{6}{11}\)

4: \(=\dfrac{7}{19}\left(\dfrac{5}{13}+\dfrac{8}{13}-1\right)=-2\cdot\dfrac{7}{19}=-\dfrac{14}{19}\)

5: \(=\dfrac{2}{7}\left(\dfrac{4}{23}-\dfrac{27}{23}+1\right)=0\)

6: \(=\dfrac{3}{8}\left(\dfrac{3}{7}+\dfrac{4}{7}\right)+\dfrac{11}{8}=\dfrac{3}{8}+\dfrac{11}{8}=\dfrac{14}{8}=\dfrac{7}{4}\)

x x - 4/7 = 15/20  

(hình như sai đề, tại vì lớp 4 chưa học lũy thừa)
x * 2/7 -2/3 =1/2

x* 2/7 = 1/2 + 2/3

x* 2/7 = 7/6

x= 7/6 : 2/7

x= 49/12
x : 5/4 + 4/5 =2

x: 5/4 = 2 - 4/5

x: 5/4 = 6/5

x= 6/5 * 5/4

x= 3/2 

4/3 x 7/8 x 5 

= 7/6 x 5

= 35/6
8/9 x 6/5 x 2/3

= 16/15 x 2/3

= 32/45 
4/7 : 5/7 x 10/11

= 4/5 x 10/11

= 8/11
8/13 : 7/13 : 4

= 8/7 : 4

= 2/7

a

=> \(x=\dfrac{2}{7}:\dfrac{2}{3}=\dfrac{2.3}{2.7}=\dfrac{3}{7}\)

b

=> \(x=\dfrac{2}{5}:\dfrac{3}{5}=\dfrac{2.5}{3.5}=\dfrac{2}{3}\)

c

=> \(x=\dfrac{13}{7}.\dfrac{8}{13}=\dfrac{13.8}{7.13}=\dfrac{8}{7}\)

d

=> \(x=\dfrac{3}{2}:\dfrac{7}{4}=\dfrac{3.2.2}{2.7}=\dfrac{6}{7}\)

a: 2/3*x=2/7

=>x=2/7:2/3=3/7

b: x*3/5=2/5

=>x=2/5:3/5=2/5*5/3=10/15=2/3

c: x:8/13=13/7

=>x=13/7*8/13=8/7

d: 3/2:x=7/4

=>x=3/2:7/4=3/2*4/7=12/14=6/7

a) \(\dfrac{2}{3}\cdot x=\dfrac{2}{7}\)

\(\Rightarrow x=\dfrac{2}{7}:\dfrac{2}{3}\)

\(\Rightarrow x=\dfrac{2}{7}\cdot\dfrac{3}{2}\)

\(\Rightarrow x=\dfrac{3}{7}\)

b) \(x\cdot\dfrac{3}{5}=\dfrac{2}{5}\)

\(\Rightarrow x=\dfrac{2}{5}:\dfrac{3}{5}\)

\(\Rightarrow x=\dfrac{2}{5}\cdot\dfrac{5}{3}\)

\(\Rightarrow x=\dfrac{2}{3}\)

c) \(x:\dfrac{8}{13}=\dfrac{13}{7}\)

\(\Rightarrow x=\dfrac{8}{13}\cdot\dfrac{13}{7}\)

\(\Rightarrow x=\dfrac{8}{7}\)

d) \(\dfrac{3}{2}:x=\dfrac{7}{4}\)

\(\Rightarrow x=\dfrac{3}{2}:\dfrac{7}{4}\)

\(\Rightarrow x=\dfrac{3}{2}\cdot\dfrac{4}{7}\)

\(\Rightarrow x=\dfrac{6}{7}\)

Câu 13 :

\(\left(-\frac{1}{4}+\frac{5}{8}\right)+-\frac{3}{5}\)

\(=\frac{3}{8}-\frac{-3}{5}\)

\(=\frac{39}{40}\)

Câu 14 :

\(M=\frac{5}{9}.\frac{7}{13}+\frac{5}{9}.\frac{9}{13}-\frac{5}{9}.\frac{3}{13}\)

\(=\frac{5}{9}.\left(\frac{7}{13}+\frac{9}{13}-\frac{3}{13}\right)\)

\(=\frac{5}{9}.1=\frac{5}{9}\)

Câu 15 :

\(E=\left(-\frac{3}{4}+\frac{2}{5}\right):\frac{3}{7}+\left(\frac{3}{5}+\frac{-1}{4}\right):\frac{3}{7}\)

\(E=\left(-\frac{3}{4}+\frac{2}{5}+\frac{3}{5}+\frac{-1}{4}\right):\frac{3}{7}\)

\(E=0\)

Câu 16 :

\(H=\frac{7}{8}:\left(\frac{2}{9}-\frac{1}{8}\right)+\frac{7}{8}:\left(\frac{1}{36}-\frac{5}{12}\right)\)

\(=\frac{7}{8}:\left(\frac{2}{9}-\frac{1}{8}+\frac{1}{36}-\frac{5}{12}\right)\)

\(=\frac{7}{8}:\frac{-7}{24}=-3\)

huhuhuhuhuhuhuhuhuhuhuhuhu giúp mk đi 

Plssssssssssssssssssssssssssssssssssssssssssssss

Câu 14:

M =  \(\frac{5}{9}\) \(.\) \(\frac{7}{13}\) \(+\) \(\frac{5}{9}\) \(.\) \(\frac{9}{13}\) \(-\) \(\frac{5}{9}\) \(.\) \(\frac{3}{13}\)

M =    \(\frac{5}{9}\)  \(.\) (   \(\frac{7}{13}\)\(+\) \(\frac{9}{13}\) \(-\) \(\frac{3}{13}\))

M =      \(\frac{5}{9}\)  \(.\)    \(1\)

M  =              \(\frac{5}{9}\)

a) \(\frac{18}{45}-\frac{4}{12}-\frac{6}{9}-\frac{21}{35}=\frac{2}{5}-\frac{1}{3}-\frac{2}{3}-\frac{3}{5}\)

\(=\left(\frac{2}{5}-\frac{3}{5}\right)-\left(\frac{1}{3}+\frac{2}{3}\right)\)

\(=\frac{-1}{3}-1\)

\(=\frac{-4}{3}\)

b) \(\frac{4}{3}+\frac{3}{5}+\frac{7}{3}+\frac{2}{5}+\frac{1}{3}=\left(\frac{4}{3}+\frac{7}{3}+\frac{1}{3}\right)+\left(\frac{3}{5}+\frac{2}{5}\right)\)

\(=4+1=5\)

c) \(\frac{1}{3}.\frac{4}{5}.\frac{1}{3}.\frac{6}{5}=\frac{8}{75}\)

d) \(\frac{6}{7}.\frac{8}{13}+\frac{6}{7}.\frac{9}{13}-\frac{3}{13}.\frac{6}{7}\)

\(=\frac{6}{7}.\left(\frac{8}{13}+\frac{9}{13}-\frac{3}{13}\right)\)

\(=\frac{6}{7}.\frac{14}{13}\)

\(=\frac{12}{13}\)

= 8/13x(4/7+3/7)

=8/13x1

=8/13

\(\frac{4}{7}\times\frac{8}{13}+\frac{8}{13}\times\frac{3}{7}\)

\(=\frac{8}{13}\times\left(\frac{4}{7}+\frac{3}{7}\right)\)

\(=\frac{8}{13}\times1\)

\(=\frac{8}{13}\)

P/s tham khảo nha

= 8/ 13 NHA 

HT

a) x=3/7

b)x=8/7

c)x=6/7

a)\(x=\dfrac{2}{7}:\dfrac{2}{3}=\dfrac{3}{7}\)

b)\(x=\dfrac{13}{7}\times\dfrac{8}{13}=\dfrac{8}{7}\)

c)\(x=\dfrac{3}{2}:\dfrac{7}{4}=\dfrac{6}{7}\)

=3/7

=8/7

=6/7