a) https://hoc247.net/hoi-dap/toan-7/thuc-hien-phep-tinh-5-5-27-7-23-0-5-5-27-16-23-faq218258.html

b) https://hoidap247.com/cau-hoi/1507941

b) \(\dfrac{10^9.49^4}{14^8.25^5}=\dfrac{\left(2.5\right)^9.\left(7^2\right)^4}{\left(7.2\right)^8.\left(5^2\right)^5}=\dfrac{2^9.5^9.7^6}{7^8.2^8.5^{10}}=\dfrac{2}{7.7.5}=\dfrac{2}{245}\)

\(a,=\left(\dfrac{140}{27}+\dfrac{1}{2}\cdot\dfrac{5}{27}\right)+\left(\dfrac{7}{23}+\dfrac{16}{23}\right)\\ =\left(\dfrac{140}{27}+\dfrac{5}{54}\right)+1=\dfrac{285}{54}+1=\dfrac{339}{54}=\dfrac{113}{18}\\ b,=\dfrac{2^9\cdot5^9\cdot7^8}{7^8\cdot2^8\cdot5^{10}}=\dfrac{2}{5}\)

a ( ....< ....)

b( ....<....)

a <

b <

tick cho mk nha

\(a,\dfrac{x}{7}=\dfrac{6}{12}\\ x\cdot12=7\cdot6=42\\ x=42:12\\ x=\dfrac{7}{2}\\ b,\dfrac{-5}{x}=\dfrac{20}{28}\\ x\cdot20=\left(-5\right)\cdot28=-140\\ x=\left(-140\right):20\\ x=-7\\ c,\dfrac{x-2}{8}=\dfrac{3}{4}\\ \left(x-2\right)4=8\cdot3=24\\ x-2=24:4\\ x-2=6\\ x=6+2\\ x=8\\ d,\dfrac{x}{-5}=\dfrac{-5}{x}\\ x^2=\left(-5\right)\cdot\left(-5\right)=25\\ x=5\)

\(\dfrac{2}{1\times3}+\dfrac{2}{3\times5}+\dfrac{2}{5\times7}+...+\dfrac{2}{13\times15}+\dfrac{2}{15\times17}\)

\(=1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{13}-\dfrac{1}{15}+\dfrac{1}{15}-\dfrac{1}{17}\)

\(=1-\dfrac{1}{17}\)

\(=\dfrac{16}{17}\)

\(\dfrac{2}{1\cdot3}+\dfrac{2}{3\cdot5}+...+\dfrac{2}{15\cdot17}\)

\(=2-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{15}-\dfrac{1}{17}\)

\(=2-\dfrac{1}{17}\)

\(=\dfrac{33}{17}\)

MSC : `24`

`-5/6=-5.4/6.4=-20/24`

`7/8=7.3/8.3=21/24`

`7/24=7/24`

`-3/4=-3.6/4.6=-18/24`

`2/3=2.8/3.8=16/24`

`1=24/24`

Sắp xếp các phân số sau theo thứ tự tăng dần : 

`-20/24;-18/24;7/24;16/24;21/24;24/24`

\(\dfrac{6}{7}+\dfrac{5}{8}=\dfrac{48}{56}+\dfrac{35}{56}=\dfrac{83}{56}\)

\(\dfrac{36}{12}-\dfrac{5}{3}=\dfrac{9}{3}-\dfrac{5}{3}=\dfrac{4}{3}\)

\(\dfrac{6}{7}+\dfrac{5}{8}=\dfrac{48}{56}+\dfrac{35}{56}=\dfrac{83}{56}\\\dfrac{36}{12}+\dfrac{5}{3}=\dfrac{36}{12}+\dfrac{20}{12} =\dfrac{56}{12}=\dfrac{14}{3}\)

6/7 + 5/8 = 48/56 + 35/56 = 83/56

36/12 - 5/3 = 36/12 - 20/12 = 16/12 = 4/3

( 5/7 + x ) : 4/9 = 2/3

  5/7 + x           = 2/3 x 4/9

  5/7 + x           = 8/27

           x            = 8/27 - 5/7

           x            = -79/189

Mình tính được bài bạn nhưng hình như bạn làm sai đề hay sao mà mình làm ra âm luôn ! Mà âm thì chưa học lớp 5 , mong bạn xem lại đề xem có sai không nhé ! 

`1/5 . 4/7 + 3/7 . 1/5 -1/5`

`=1/5 . 4/7 + 3/7 . 1/5 -1/5 . 1`

`=1/5 . ( 4/7+3/7-1)`

`=1/5 . ( 7/7-1)`

`= 1/5 . 0`

`=0`

\(\dfrac{1}{5}\times\dfrac{4}{7}+\dfrac{3}{7}\times\dfrac{1}{5}-\dfrac{1}{5}=\dfrac{1}{5}\times\left(\dfrac{4}{7}+\dfrac{3}{7}-1\right)=\dfrac{1}{5}\times0=0\)

= \(\dfrac{1}{5}\).(\(\dfrac{4}{7}\)+\(\dfrac{3}{7}\)+1)

= \(\dfrac{1}{5}\)+ 0

\(\dfrac{1}{5}\)

\(\dfrac{-1}{9}.\dfrac{-3}{5}+\dfrac{5}{-6}.\dfrac{-3}{5}-\dfrac{7}{2}.\dfrac{3}{5}\)

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

\(=\dfrac{3}{5}.\left(\dfrac{2}{18}+\dfrac{15}{18}-\dfrac{63}{18}\right)\)

\(=\dfrac{3}{5}.\left(-\dfrac{23}{9}\right)\)

\(=-\dfrac{69}{45}\)