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30 tháng 6 2021

\(2.\frac{3}{7}\left(\frac{2}{9}.1\frac{3}{7}\right)-\frac{5}{9}:\frac{1}{9}\)

\(=2.\frac{3}{7}+\left(\frac{2}{9}-\frac{10}{7}\right)-\frac{5}{9}.9\)

\(=\frac{6}{7}+\frac{2}{9}-\frac{10}{7}+\frac{45}{9}\)

\(=\frac{-4}{7}+\frac{47}{9}\)

\(=\frac{-36}{63}+\frac{329}{63}\)

\(=\frac{293}{63}\)

28 tháng 7 2018

\(2×\dfrac{3}{7}+\left(\dfrac{2}{9}-\dfrac{10}{7}\right)-\dfrac{5}{3}:\dfrac{1}{9}\)

\(=\dfrac{6}{7}+\dfrac{2}{9}-\dfrac{10}{7}-15\)

\(=\left(\dfrac{6}{7}-\dfrac{10}{7}\right)+\dfrac{2}{9}-15\)

\(=-\dfrac{4}{7}+\dfrac{2}{9}-15\)

\(=-\dfrac{22}{63}-15\)

\(=-\dfrac{967}{63}\)

26 tháng 7 2018

\(2x.\dfrac{3}{7}+\left(\dfrac{2}{9}+\dfrac{10}{7}\right)-\dfrac{5}{3}:\dfrac{1}{9}\)

\(\Leftrightarrow2x\dfrac{3}{7}+\dfrac{2}{9}-\dfrac{10}{7}-\dfrac{5}{3}:\dfrac{1}{9}\)

\(\Leftrightarrow\dfrac{6x}{7}+\dfrac{2}{9}-\dfrac{10}{7}-\dfrac{5}{3}:\dfrac{1}{9}\)

\(\Leftrightarrow\dfrac{6x}{7}+\dfrac{2}{9}-\dfrac{10}{7}-15\)

\(\Leftrightarrow\dfrac{6x}{7}-\dfrac{1021}{63}\)

Giải:

A=5/9+2/15-6/9

   =(5/9-6/9)+2/15

   = -1/9 + 2/15

   = 1/45

B=2/7-3/8+4/7+1/7-5/8+5/15

   = (2/7+4/7+1/7) + (-3/8-5/8) +1/3

   = 1+ (-1) +1/3

   =1/3

C=3/5+1/15+1/57+1/3-2/9-3/4-1/36

   =9/15+1/15+1/57+19/57-8/36-27/36-1/36

   =(9/15+1/15)+(1/57+19/57)+(-8/36-27/36-1/36)

   =2/3+20/57+(-1)

   =58/57+(-1)

   =1/57

D=1/1.2+1/2.3+1/3.4+...+1/99.100

   =1/1-1/2+1/2-1/3+1/3-1/4+...+1/99-1/100

   =1/1-1/100

   =99/100

Câu E mình ko biết làm nhé!

11 tháng 7 2016

bằng 13/15 bạn ạ 

27 tháng 3 2018

\(\frac{1}{7}.\frac{5}{9}+\frac{5}{9}.\frac{1}{7}+\frac{5}{9}.\frac{3}{7}\)

\(=\frac{5}{9}.\left(\frac{1}{7}+\frac{1}{7}+\frac{3}{7}\right)\)

\(=\frac{5}{9}.\frac{5}{7}=\frac{25}{63}\)

học vui!

27 tháng 3 2018

= 5/9 . ( 1/7 + 1/7 + 3/7 )

= 5/9 . 5/7

= 25/63

Tk nha !!

9 tháng 8 2016

a) 3/7 + 4/9 + 4/7 + 5/9

= ( 3/7 + 4/7 ) + ( 4/9 + 5/9 )

= 7/7 + 9/9

= 1  + 1 

= 2

b)1/5 + 4/10 + 9/15 + 16/20 + 25/25 + 36/30 + 49/35 + 64/40 + 81/45

= 1/5 + 2/5 + 3/5 + 4/5 + 5/5 + 6/5 + 7/5 + 8/5 + 9/5

= ( 1/5 + 9/5 ) + ( 2/5 + 8/5 ) + (7/5 + 3/5 ) + ( 4/5 + 6/5  ) + 5/5

= 2 + 2 + 2 + 2 + 1

= 2  x 4 + 1

= 8  +1 

= 9

c)  1/8 + 1/12 + 3/8 + 5/12

= ( 1/8 + 3/8 ) + ( 1/12 + 5/12)

= 4/8 + 6/12

= 1/2 + 1/2

= 2/4 = 1/2

mỏi tay rồi

22 tháng 9

d; (1 - \(\dfrac{1}{2}\)) x (1 - \(\dfrac{1}{3}\)) x (1 - \(\dfrac{1}{4}\)) x ... x ( 1 - \(\dfrac{1}{100}\))

 = \(\dfrac{1}{2}\) x \(\dfrac{2}{3}\)  x \(\dfrac{3}{4}\) x \(\dfrac{3}{4}\) x ... x \(\dfrac{99}{100}\)

\(\dfrac{1}{100}\)

 

21 tháng 2 2023

\(\dfrac{1}{7}.\dfrac{5}{9}+\dfrac{5}{7}.\dfrac{1}{9}+\dfrac{5}{9}.\dfrac{3}{7}=\dfrac{5}{9}.\left(\dfrac{1}{7}+\dfrac{3}{7}\right)+\dfrac{5}{7}.\dfrac{1}{9}\\ =\dfrac{5}{9}.\dfrac{4}{7}+\dfrac{5}{7}.\dfrac{1}{9}=\dfrac{20}{63}+\dfrac{5}{63}=\dfrac{25}{63}\)

21 tháng 2 2023

\(\dfrac{1}{7}.\dfrac{5}{9}+\dfrac{5}{7}.\dfrac{5}{9}+\dfrac{5}{9}.\dfrac{3}{7}\)

\(=\dfrac{5}{9}.\left(\dfrac{1}{7}+\dfrac{5}{7}+\dfrac{3}{7}\right)\)

\(=\dfrac{5}{9}.\dfrac{9}{7}\)

\(=\dfrac{5}{7}\)

2 tháng 4 2019

\(N=\frac{1}{6}.\frac{5}{9}+\frac{5}{9}.\frac{2}{7}+\frac{1}{9}.\frac{5}{7}-\frac{5}{9}.\frac{3}{7}\)

\(N=\frac{1}{6}.\left(\frac{5}{9}+\frac{1}{9}\right).\left(\frac{2}{7}+\frac{5}{7}-\frac{3}{7}\right)\)

\(N=\frac{1}{6}.\frac{6}{9}.\frac{4}{7}\)

\(N=\frac{1}{9}.\frac{4}{7}\)

\(N=\frac{4}{63}\)

12 tháng 6 2020

\(N=\frac{1}{6}.\frac{5}{9}+\frac{5}{9}.\frac{2}{7}+\frac{1}{9}.\frac{5}{7}-\frac{5}{9}.\frac{3}{7}\)

\(N=\frac{1}{6}.\frac{5}{9}+\frac{5}{9}.\frac{2}{7}+\frac{5}{9}.\frac{1}{7}-\frac{5}{9}.\frac{3}{7}\)

\(N=\frac{5}{9}.\left(\frac{1}{6}+\frac{2}{7}+\frac{1}{7}-\frac{3}{7}\right)\)

\(N=\frac{5}{9}.\frac{1}{6}\)

\(N=\frac{5}{54}\)

21 tháng 3 2017

A=1                                                                                                                                                                                                  B=-4