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`#3107.101107`

`1.`

`a)`

\(\dfrac{7}{23}-\dfrac{5}{14}+\dfrac{1}{2}-\dfrac{9}{14}+\dfrac{16}{23}\\ =\left(\dfrac{7}{23}+\dfrac{16}{23}\right)-\left(\dfrac{5}{14}+\dfrac{9}{14}\right)+\dfrac{1}{2}\\ =\dfrac{23}{23}-\dfrac{14}{14}+\dfrac{1}{2}\\ =1-1+\dfrac{1}{2}\\ =\dfrac{1}{2}\)

`b)`

\(\left(-\dfrac{2}{3}\right)\cdot\dfrac{3}{11}+\left(-\dfrac{16}{9}\right)\cdot\dfrac{3}{11}\\ =\dfrac{3}{11}\cdot\left(-\dfrac{2}{3}-\dfrac{16}{9}\right)\\ =\dfrac{3}{11}\cdot\left(-\dfrac{22}{9}\right)\\ =-\dfrac{2}{3}\)

`2.`

`a)`

\(-\dfrac{3}{7}x=\dfrac{1}{2}-\dfrac{1}{3}\\ \Rightarrow-\dfrac{3}{7}x=\dfrac{1}{6}\\ \Rightarrow x=\dfrac{1}{6}\div\left(-\dfrac{3}{7}\right)\\ \Rightarrow x=-\dfrac{7}{18}\)

`b)`

\(\left(x+\dfrac{1}{2}\right)^2=\dfrac{1}{16}\\ \Rightarrow\left(x+\dfrac{1}{2}\right)^2=\left(\pm\dfrac{1}{4}\right)^2\\ \Rightarrow\left[{}\begin{matrix}x+\dfrac{1}{2}=\dfrac{1}{4}\\x+\dfrac{1}{2}=-\dfrac{1}{4}\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=\dfrac{1}{4}-\dfrac{1}{2}\\x=-\dfrac{1}{4}-\dfrac{1}{2}\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=-\dfrac{1}{4}\\x=-\dfrac{3}{4}\end{matrix}\right.\)

_____

`1.`

`a)`

\(-\dfrac{9}{17}+6,72+\dfrac{-8}{17}+\left(-4,72\right)\\ =\left(-\dfrac{9}{17}-\dfrac{8}{17}\right)+\left(6,72-4,72\right)\\ =-\dfrac{17}{17}+2\\ =-1+2=1\)

`b)`

\(2\dfrac{1}{5}-\left(-\dfrac{3}{4}+\dfrac{1}{5}\right)\\ =\dfrac{11}{5}+\dfrac{3}{4}-\dfrac{1}{5}\\ =\left(\dfrac{11}{5}-\dfrac{1}{5}\right)+\dfrac{3}{4}\\ =\dfrac{10}{5}-\dfrac{3}{4}\\ =2-\dfrac{3}{4}\\ =\dfrac{5}{4}\)

`c)`

\(\left(-\dfrac{1}{3}\right)^3-\dfrac{3}{8}\div \left(\dfrac{1}{2}\right)^3-\dfrac{5}{2}\cdot\left(-2\right)\\ =\left(-\dfrac{1}{27}\right)-\dfrac{3}{8}\div\dfrac{1}{8}-\left(-5\right)\\ =-\dfrac{1}{27}-3+5\\ =-\dfrac{1}{27}+2\\ =\dfrac{53}{27}\)

`d)`

\(4,1\cdot\dfrac{-5}{12}-6,2+4,1\cdot\dfrac{-7}{12}\\ =4,1\cdot\left(-\dfrac{5}{12}-\dfrac{7}{12}\right)-6,2\\ =4,1\cdot\left(-\dfrac{12}{12}\right)-6,2\\ 4,1\cdot\left(-1\right)-6,2\\ =-4,1-6,2\\ =-10,3\)

`2.`

`a)`

\(x+\left(-\dfrac{1}{9}\right)=-\dfrac{7}{6}\\ \Rightarrow x=-\dfrac{7}{6}-\left(-\dfrac{1}{9}\right)\\ \Rightarrow x=-\dfrac{7}{6}+\dfrac{1}{9}\\ \Rightarrow x=-\dfrac{19}{18}\)

`b)`

\(\left(x-\dfrac{4}{7}\right)\div\dfrac{-5}{3}=0,2\\ \Rightarrow x-\dfrac{4}{7}=0,2\cdot\left(-\dfrac{5}{3}\right)\\ \Rightarrow x-\dfrac{4}{7}=-\dfrac{1}{3}\\ \Rightarrow x=-\dfrac{1}{3}+\dfrac{4}{7}\\ \Rightarrow x=\dfrac{5}{21}\)

`c)`

\(\left(2x-\dfrac{1}{3}\right)^3=\dfrac{1}{8}\\ \Rightarrow\left(2x-\dfrac{1}{3}\right)^3=\left(\dfrac{1}{2}\right)^3\\ \Rightarrow2x-\dfrac{1}{3}=\dfrac{1}{2}\\ \Rightarrow2x=\dfrac{1}{2}+\dfrac{1}{3}\\ \Rightarrow2x=\dfrac{5}{6}\\ \Rightarrow x=\dfrac{5}{6}\div2\\ \Rightarrow x=\dfrac{5}{12}\)

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`13.`

`a)`

Ta có: \(\dfrac{139}{303}>\dfrac{138}{303}=\dfrac{46}{101}\)

Mà \(\dfrac{35}{101}< \dfrac{46}{101}\)

\(\Rightarrow\dfrac{139}{303}>\dfrac{35}{101}\)

`b)`

Ta có:

\(\left(\dfrac{1}{2}\right)^8\div\left(\dfrac{1}{2}\right)^2=\left(\dfrac{1}{2}\right)^{8-2}=\left(\dfrac{1}{2}\right)^6\)

\(\left(\dfrac{1}{2}\right)^3\cdot\left(\dfrac{1}{2}\right)^3=\left(\dfrac{1}{2}\right)^{3+3}=\left(\dfrac{1}{2}\right)^6\)

Vì \(\left(\dfrac{1}{2}\right)^6=\left(\dfrac{1}{2}\right)^6\\ \Rightarrow\left(\dfrac{1}{2}\right)^8\div\left(\dfrac{1}{2}\right)^2=\left(\dfrac{1}{2}\right)^3\cdot\left(\dfrac{1}{2}\right)^3\)

`14.`

`a)`

\(-\dfrac{11}{24}+\dfrac{3}{4}-\dfrac{13}{24}\\ =\left(-\dfrac{11}{24}-\dfrac{13}{24}\right)+\dfrac{3}{4}\\ =-\dfrac{24}{24}+\dfrac{3}{4}\\ =-1+\dfrac{3}{4}\\ =-\dfrac{1}{4}\)

`b)`

\(-\dfrac{5}{9}-\left(\dfrac{8}{15}+\dfrac{4}{9}\right)+\dfrac{7}{15}\\ =-\dfrac{5}{9}-\dfrac{8}{15}-\dfrac{4}{9}+\dfrac{7}{15}\\ =\left(-\dfrac{5}{9}-\dfrac{4}{9}\right)-\left(\dfrac{8}{15}+\dfrac{7}{15}\right)\\ =-\dfrac{9}{9}-\dfrac{15}{15}\\ =-1-1=-2\)

`c)`

\(\dfrac{5}{9}\div2,4-\dfrac{41}{9}\div2,4\\ =\dfrac{5}{9}\div\dfrac{12}{5}-\dfrac{41}{9}\div\dfrac{12}{5}\\ =\dfrac{5}{9}\cdot\dfrac{5}{12}-\dfrac{41}{9}\cdot\dfrac{5}{12}\\ =\dfrac{5}{12}\cdot\left(\dfrac{5}{9}-\dfrac{41}{9}\right)\\ =\dfrac{5}{12}\cdot\left(-\dfrac{36}{9}\right)\\ =\dfrac{5}{12}\cdot\left(-4\right)\\ =-\dfrac{5}{3}\)

`a)`

`b)`

`c)`

a: =>x-4=0 hoặc x+5=0

=>x=4 hoặc x=-5

b: =>39/7:x=13

hay x=3/7

c: \(\Leftrightarrow\left(4.5-2x\right)=\dfrac{11}{4}:\dfrac{4}{9}=\dfrac{99}{16}\)

\(\Leftrightarrow2x=-\dfrac{27}{16}\)

hay x=-27/32

d: \(\Leftrightarrow x\cdot\dfrac{19}{15}=684\)

hay x=540

6 tháng 2 2022

a. \(\left[{}\begin{matrix}x-4=0\\x+5=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=4\\x=-5\end{matrix}\right.\)

b.\(\Leftrightarrow\dfrac{39}{7}:x=13\)

\(\Leftrightarrow x=13.\dfrac{39}{7}\)

\(\Leftrightarrow x=\dfrac{507}{7}\)

c.\(\Leftrightarrow4,5-2x=\dfrac{99}{16}\)

\(\Leftrightarrow-2x=\dfrac{27}{16}\)

\(\Leftrightarrow x=-\dfrac{27}{32}\)

15 tháng 10 2021

Bài 5:

a) Do \(x,y\in N\)

\(\Rightarrow\left\{\left(x;y-2\right)\right\}\in\left\{\left(1;7\right),\left(7;1\right)\right\}\)

\(\Rightarrow\left(x;y\right)\in\left\{\left(1;9\right),\left(7;3\right)\right\}\)

b) Do \(x,y\in N\)

\(\Rightarrow\left(x+1;y+5\right)\in\left\{\left(1;12\right),\left(2;6\right)\right\}\)

\(\Rightarrow\left(x;y\right)\in\left\{\left(0;7\right),\left(1;1\right)\right\}\)

c) Do \(x,y\in N\)

\(\Rightarrow\left(x-1;2y+1\right)\in\left\{\left(18;1\right),\left(2;9\right),\left(6;3\right)\right\}\)

\(\Rightarrow\left(x;y\right)\in\left\{\left(19;0\right),\left(3;4\right),\left(7;1\right)\right\}\)

 

9 tháng 5 2022

\(A=10^2\times\left[\left(-2\right).10,1-20,21+2.10,11\right]\)

\(=100\times\left[\left(-20,2\right)-20,21+20,22\right]\)

\(=-20,19\times100=-2019\)

19 tháng 2 2023

\(\dfrac{x-2}{5}=\dfrac{1-x}{6}\\ =>\left(x-2\right)\cdot6=\left(1-x\right)\cdot5\\ =>6x-12=5-5x\\ =>6x+5x=5+12\\ =>11x=17\\ x=\dfrac{17}{11}\)

19 tháng 2 2023

`[x-2]/5=[1-x]/6`

`=>6(x-2)=5(1-x)`

`=>6x-12=5-5x`

`=>6x+5x=5+12`

`=>11x=17`

`=>x=17/11`

a: =>x=75:25%=300

b: =>11/12x=-7/12

hay x=-7/11

c: \(\Leftrightarrow\left(x-1\right)\cdot\dfrac{1}{4}=\dfrac{1}{2}-\dfrac{3}{4}=\dfrac{-1}{4}\)

=>x-1=-1

hay x=0

6 tháng 2 2022

\(a,=0,25.x=75\Rightarrow x=75:0,25=300\)

\(b,\dfrac{11}{12}x=\dfrac{1}{6}-\dfrac{3}{4}=\dfrac{-7}{12}\)

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

\(c,\dfrac{1}{4}\left(x-1\right)=\dfrac{1}{2}-\dfrac{3}{4}=\dfrac{-1}{4}\)

\(x-1=\dfrac{-1}{4}:\dfrac{1}{4}=-1\)

\(\Leftrightarrow x=0\)

10 tháng 7 2023

A 1287

b 31/13

 

10 tháng 7 2023

câu c, d đâu ròi bn ? câu a, b giải chi tiết ra bn nhé

Thấy gì đâu??

25 tháng 3 2022

._.?

18 tháng 10 2021

14.D

15.B

16.C

18 tháng 10 2021

d b c

13 tháng 1 2022

lỗi rồi

13 tháng 1 2022

lỗi