=>2x=5,8

hay x=2,9

x=2,9

=5,8(1+3+5+1)=58

=5.8 x (3+5)
=5.8 x 8
=29

5,8 + 5.8 x 3 + 5.8 x 5 + 5.8

= 5,8 + 5.8 x 3 + 5.8 x 5 + 5.8 x 1

= 5,8 x 1 + 5.8 x 3 + 5.8 x 5 + 5.8 x 1

= 5,8 x (1+3+5+1)

= 5.8 x 10

= 58

a) 2/2.5 + 2/5.8 + 2/8.11 + ... + 2/x(x+3) = 7/23

3/2.5 + 3/5.8 + 3/8.11 + ... + 3/x(x+3) = 21/46

1/2 - 1/5 + 1/5 - 1/8 + 1/8 - 1/11 + ... + 1/x - 1/x+1 = 21/46

1/2 - 1/x+1 = 21/46

=> 1/x+1 = 1/23

=> x + 1 = 23

=> x = 22

Vậy x = 22.

b) 3/4 . x - 1/5 = 7/4 . x + 11/5

3/4 . x - 7/4 . x = 1/5 + 11/5

x (3/4 - 7/4) = 12/5

-x = 12/5

x = -12/5

Vậy x = -12/5.

\(\frac{4}{2\cdot5}+\frac{4}{5\cdot8}+...+\frac{4}{x\cdot\left(x+3\right)}=\frac{22}{35}\)

\(\frac{3}{2\cdot5}+\frac{3}{5\cdot8}+...+\frac{3}{x\cdot\left(x+3\right)}=\frac{33}{70}\)

\(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+...+\frac{1}{x}-\frac{1}{x+3}=\frac{33}{70}\)

\(\frac{1}{2}-\frac{1}{x+3}=\frac{33}{70}\)

\(\frac{1}{x+3}=\frac{1}{35}\)

\(\Rightarrow x+3=35\)

\(\Rightarrow x=32\)

\(\frac{4}{2\cdot5}+\frac{4}{5\cdot8}+...+\frac{4}{x\left(x+3\right)}=\frac{22}{35}\)

\(\frac{3}{4}\left(\frac{4}{2\cdot5}+\frac{4}{5\cdot8}+...+\frac{4}{x\left(x+3\right)}\right)=\frac{3}{4}\cdot\frac{22}{35}\)

\(\frac{3}{2\cdot5}+\frac{3}{5\cdot8}+...+\frac{3}{x\left(x+3\right)}=\frac{33}{70}\)

\(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+...+\frac{1}{x}-\frac{1}{x+3}=\frac{33}{70}\)

\(\frac{1}{2}-\frac{1}{x+3}=\frac{33}{70}\)

\(\frac{1}{x+3}=\frac{1}{35}\)

\(\Rightarrow x+3=35\)

\(\Rightarrow x=32\)

Vậy x=32

\(\frac{4}{2.5}+\frac{4}{5.8}+...+\frac{4}{x\left(x+3\right)}=\frac{22}{35}\)

\(\Rightarrow\)\(\frac{3}{4}.\left(\frac{4}{2.5}+\frac{4}{5.8}+...+\frac{4}{x\left(x+3\right)}\right)=\frac{3}{4}.\frac{22}{35}\)

\(\Rightarrow\)\(\frac{3}{2.5}+\frac{3}{5.8}+...+\frac{3}{x\left(x+3\right)}=\frac{33}{70}\)

\(\Rightarrow\)\(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+...+\frac{1}{x}-\frac{1}{x+3}=\frac{33}{70}\)

\(\Rightarrow\)\(\frac{1}{2}-\frac{1}{x+3}=\frac{33}{70}\)

\(\Rightarrow\)\(\frac{1}{x+3}=\frac{1}{2}-\frac{33}{70}\)

\(\Rightarrow\)\(\frac{1}{x+3}=\frac{1}{35}\)

\(\Rightarrow\)\(x+3=35\)

\(\Rightarrow\)\(x=35-3\)

\(\Rightarrow\)\(x=32\)

\(\text{-7129+1478+7129+(-1479)}\)

\(=\text{-7129+7129+1478+(-1479)}\)

\(=0-1=-1\)

\(\text{|-5|.(-7)+4.(-9)}\)

\(=\text{5.(-7)+4.(-9)}\)

\(=\left(-35\right)+\left(-36\right)=-71\)

\(\text{(-4)²+35:(-7)}\)

\(=\text{16+(-5)=11}\)

x.\(\left(\frac{3}{2.5}+\frac{3}{5.8}+\frac{3}{8.11}+\frac{3}{11.14}+\frac{3}{14.17}\right)=-1\frac{3}{5}\)

x.\(\left(\frac{5-2}{2.5}+\frac{8-5}{5.8}+\frac{11-8}{8.11}+\frac{14-11}{11.14}+\frac{17-14}{14.17}\right)=\frac{-8}{5}\)

x.\(\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{17}\right)=\frac{-8}{5}\)

x.\(\left(\frac{1}{2}-\frac{1}{17}\right)=\frac{-8}{5}\)

x.\(\left(\frac{17}{34}-\frac{2}{34}\right)=\frac{-8}{5}\)

x.\(\frac{15}{34}=\frac{-8}{5}\)

x\(=\frac{-8}{5}:\frac{15}{34}\)

x\(=\frac{-8}{5}.\frac{34}{15}\)

x\(=\frac{-272}{75}\)

Vậy x\(=\frac{-272}{75}\)

\(\left(x-3\right)^2+\frac{-9}{25}=\frac{2}{5}.\frac{8}{5}\)

\(\left(x-3\right)^2+\frac{-9}{25}=\frac{16}{25}\)

\(\left(x-3\right)^2=\frac{16}{25}+\frac{-9}{25}\)

\(\left(x-3\right)^2=\frac{7}{25}\)

\(\left(x-3\right)^2=\left(\frac{7}{5}\right)^2\)

\(\Rightarrow x-3=\frac{7}{5}\)

\(\Rightarrow x=\frac{7}{5}+3\)

\(\Rightarrow x=\frac{22}{5}\)

\(\left(x-3\right)^2+\left(\frac{-9}{25}\right)=\frac{2}{5}.\frac{8}{5}\)

\(\left(x-3\right)^2+\left(\frac{-9}{25}\right)=\frac{16}{25}\)

\(\left(x-3\right)^2=1=1^2\)

\(\Rightarrow x-3=1\)

\(\Rightarrow x=4\)

P/s: Hoq chắc :<

( x - 3 )²  + \(\frac{-9}{25}=\frac{2}{5}.\frac{8}{5}\)

 ( x - 3 )²  + \(\frac{-9}{25}=\frac{16}{25}\)

( x - 3 ) ²  = \(\frac{16}{25}-\frac{-9}{25}\)

( x - 3 )² = 1² = ( -1 )² 

\(\hept{\begin{cases}x-3=-1\\x-3=1\end{cases}}=>\hept{\begin{cases}x=2\\x=4\end{cases}}\)

vậy x = 2 , 4