4/5 - (-2/7) - 7/10

= 4/5 + 2/7 - 7/10

= 8/10 - 7/10 + 2/7

= 1/10 + 2/7

= 7/70 + 20/70

= 27/70

\(\dfrac{4}{5}-\left(-\dfrac{2}{7}\right)-\dfrac{7}{10}\)

\(=\dfrac{4}{5}+\dfrac{2}{7}-\dfrac{7}{10}\)

\(=\dfrac{8-7}{10}+\dfrac{2}{7}\)

\(=\dfrac{1}{10}+\dfrac{2}{7}\)

\(=\dfrac{7+20}{70}\)

\(=\dfrac{27}{70}\)

Xin lỗi m.n nhé gửi nhầm tí

a: \(\dfrac{1}{8}\cdot\dfrac{4}{5}:\dfrac{3}{5}=\dfrac{1}{10}\cdot\dfrac{5}{3}=\dfrac{1}{2\cdot3}=\dfrac{1}{6}\)

b: \(=\dfrac{8-3}{12}\cdot\dfrac{6}{5}=\dfrac{6}{12}=\dfrac{1}{2}\)

c: \(=\dfrac{24}{35}:\dfrac{32}{35}=\dfrac{3}{4}\)

d: =63/21+15/21-7/21=71/21

a \(\dfrac{1}{8}\times\dfrac{4}{5}\times\dfrac{10}{6}=\dfrac{1}{6}\)

b \(\left(\dfrac{8}{12}-\dfrac{3}{12}\right)\times\dfrac{6}{5}=\dfrac{5}{12}\times\dfrac{6}{5}=\dfrac{1}{2}\)

c \(\dfrac{24}{35}:\dfrac{32}{35}=\dfrac{24}{35}\times\dfrac{35}{32}=\dfrac{3}{4}\)

d \(\dfrac{63}{21}+\dfrac{15}{21}-\dfrac{7}{21}=\dfrac{71}{21}\)

2: 

a: =>x=1/2+1/6=3/6+1/6=4/6=2/3

b: =>x+3,5=7,8-6,3=1,5

=>x=1,5-3,5=-2

c: =>(35-x)/-105=1/5

=>35-x=-21

=>x=56

1

c hình như tính bình thường thôi:v

d

= 1,75 : 5 + 2,5 . (16 – 4 . 4,1)

= 1,75 : 5 + 2,5 . (16 – 16,4)

= 1,75 : 5 + 2,5 . (−0,4)

= 0,35 − 1

= −0,65.

2

a

\(\Rightarrow x=\dfrac{1}{2}+\dfrac{1}{6}=\dfrac{3}{6}+\dfrac{1}{6}=\dfrac{4}{6}=\dfrac{2}{3}\)

b

\(\Rightarrow x+\dfrac{35}{10}=\dfrac{78}{10}-\dfrac{63}{5}:2\\ \Rightarrow x+\dfrac{35}{10}=\dfrac{78}{10}-\dfrac{63}{10}=\dfrac{15}{10}\\ \Rightarrow x=\dfrac{15}{10}-\dfrac{35}{10}=-2\)

c không rõ đề:v

\(1,\dfrac{2}{-11}.6\dfrac{2}{7}+\dfrac{3}{7}:3+5\\ =\dfrac{2}{-11}.\dfrac{44}{7}+\dfrac{3}{7}\times\dfrac{1}{3}+5\\ =-\dfrac{88}{77}+\dfrac{3}{21}+5\\ =-\dfrac{8}{7}+\dfrac{1}{7}+5\\ =-1+5\\ =4\)

\(d,1,75:5+2,5.\left(4^2-4.4,1\right)\\ =0,35+2,5.\left(16-16,4\right)\\ =0,35+2,5.0,4\\ =0,35+1\\ =1,35\)

`2,`

`a, 1/2 -x=-1/6`

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

`=> x= 1/2 +1/6`

`=> x= 3/6+1/6`

`=>x= 4/6`

`=>x=2/3`

Vậy `x=2/3`

`b, x+3,5 =7,8 -12,6 :2`

`=> x+3,5 = 7,8 - 6,3`

`=> x+3,5=1,5`

`=> x= 1,5-3,5`

`=>x=-2`

Vậy `x=-2`

\(c,\dfrac{7}{35}=\dfrac{35-x}{-105}\\ \Rightarrow7.\left(-105\right)=35.\left(35-x\right)\\ \Rightarrow-735=1225-35x\\ \Rightarrow-735-1225=-35x\\ \Rightarrow-1960=-35x\\ \Rightarrow x=-1960:\left(-35\right)\\ \Rightarrow x=56\)

Vậy `x=56`

1 +1 = 3, 3 voi 3 la 4, 4 voi 1 la ba, 3 ngon tay that deu

a. | x - 1/7 | + 3/7 = 0

<=>  | x - 1/7 | = -  3/7

Mà \(\left|x-\frac{1}{7}\right|\ge0\forall x\)

=> Không có x tm đề bài

b. | x + 1/4 | - 3/4 = 5%

<=> | x + 1/4 | = 4/5

<=> \(\orbr{\begin{cases}x+\frac{1}{4}=\frac{4}{5}\\x+\frac{1}{4}=-\frac{4}{5}\end{cases}}\)<=> \(\orbr{\begin{cases}x=\frac{11}{20}\\x=-\frac{21}{20}\end{cases}}\)

c. | - x + 2/5 | + 1/2 = 3,5

<=> | - x + 2/5 | = 3

<=> \(\orbr{\begin{cases}-x+\frac{2}{5}=3\\-x+\frac{2}{5}=-3\end{cases}}\)<=>\(\orbr{\begin{cases}x=-\frac{13}{5}\\x=\frac{17}{5}\end{cases}}\)

a) \(\left|x-\frac{1}{7}\right|+\frac{3}{7}=0\)

\(\Leftrightarrow\left|x-\frac{1}{7}\right|=-\frac{3}{7}\)

=> vô lý

PT vô nghiệm

b) \(\left|x+\frac{1}{4}\right|-\frac{3}{4}=5\%\)

\(\Leftrightarrow\left|x+\frac{1}{4}\right|=\frac{4}{5}\)

\(\Leftrightarrow\orbr{\begin{cases}x+\frac{1}{4}=\frac{4}{5}\\x+\frac{1}{4}=-\frac{4}{5}\end{cases}\Leftrightarrow}\orbr{\begin{cases}x=\frac{11}{20}\\x=-\frac{21}{20}\end{cases}}\)

c) \(\left|-x+\frac{2}{5}\right|+\frac{1}{2}=3,5\)

\(\Leftrightarrow\left|\frac{2}{5}-x\right|=3\)

\(\Leftrightarrow\orbr{\begin{cases}\frac{2}{5}-x=3\\\frac{2}{5}-x=-3\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=-\frac{13}{5}\\x=\frac{17}{5}\end{cases}}\)

a] 4/12 ; 5/12 ; 11/2 ; 1/4

b] 1 ; 9/12; 12/5 ; 11/3

c] 8/21; 6/11;8/7

d] 2/3 ;2/7 15/2

a]1/3  5/12     11/2       1/4

b]1      3/4         12/5         33/9

c]8/21      6/11        8/7

d]2/3        2/7          15/2

a) 1/3 ; 5/12 ; 11/2 ; 1/14

b) 1 ; 9/12 ; 12/5 ; 11/3

c) 8/21 ; 6/11 ; 8/7

d) 2/3 ; 2/7 ; 15/2

a,\(3:7+\left(-5:2\right)+\left(-3:5\right)\)

\(=\dfrac{3}{7}-\dfrac{5}{2}-\dfrac{3}{5}\)

\(=-\dfrac{187}{70}\)

b,\(-8:18-15:17\)

\(=-\dfrac{8}{18}-\dfrac{15}{17}\)

\(=-\dfrac{203}{153}\)

c,\(4:5-\left(-2:7\right)-7:10\)

\(=\dfrac{4}{5}-\left(-\dfrac{2}{7}\right)-\dfrac{7}{10}\)

\(=\dfrac{27}{10}\)

d,\(3,5-\left(-2:7\right)\)

\(=3,5+\dfrac{2}{7}\)

\(=\dfrac{53}{14}\)

a) | 5/4x -7/2| - | 5/8x + 3/5| = 0

|5/4x - 7/2| = | 5/8x + 3/5|

TH1: 5/4x - 7/2 = 5/8x + 3/5

=> 5/4x - 5/8x = 3/5 +7/2

5/8x = 41/10

x = 41/10:5/8

x = 164/25

TH2: 5/4x - 7/2 = -5/8x - 3/5

=> 5/4x + 5/8x  = -3/5 +7/2

15/8x  = 29/10

x = 29/10 : 15/8

x = 116/75

KL: x = 164/25 hoặc x = 116/75

các bài cn lại b lm tương tự nha! h lm dài lắm!