a) \(0,\left(31\right)+x=0,3\left(7\right)\\ \Rightarrow\dfrac{31}{99}+x=\dfrac{17}{45}\\ \Rightarrow x=\dfrac{17}{45}-\dfrac{31}{99}=\dfrac{32}{495}=0,0\left(64\right)\)

Vậy \(x=0,0\left(64\right)\)

b) \(0,\left(4\right)\cdot x=\dfrac{5}{6}\\ \Rightarrow\dfrac{4}{9}\cdot x=\dfrac{5}{6}\\ \Rightarrow x=\dfrac{5}{6}:\dfrac{4}{9}\\ \Rightarrow x=\dfrac{5}{6}\cdot\dfrac{9}{4}\\ \Rightarrow x=\dfrac{15}{8}=1,875\)

Vậy \(x=1,875\)

(x+0.5)+(x-0,2)-(-0,3) với đk x/0,3

(x+x)-(0,5-0,2+0,3)

2x-0,6=0

x=0,3

vậy ko đúng với đk

Sửa đề: \(E=\left|x+0,5\right|+\left|x-0,2\right|-\left|x-0,3\right|\)

TH1: x<-0,5

=>x+0,5<0; x-0,2<0; x-0,3<0

=>E=-x-0,5-x+0,2-(-x+0,3)

=-2x-0,3+x-0,3

=-x-0,6

TH2: -0,5<=x<0,2

=>x+0,5>=0; x-0,2<0; x-0,3<0

=>E=x+0,5+0,2-x-(0,3-x)

=0,7-0,3+x

=x+0,4

TH3: 0,2<=x<0,3

=>x+0,5>0; x-0,2>=0; x-0,3<0

=>E=x+0,5+x-0,2-(0,3-x)

=2x+0,3-0,3+x

=3x

Đáp án C

\(\left(x-0,3\right)^2=0,\left(4\right)\)

\(\Rightarrow\left(x-\frac{3}{10}\right)^2=\frac{4}{9}\)

\(\Rightarrow\left(x-\frac{3}{10}\right)^2=\left(\pm\frac{2}{3}\right)^2\)

\(\Rightarrow x-\frac{3}{10}=\pm\frac{2}{3}.\)

\(\Rightarrow\orbr{\begin{cases}x-\frac{3}{10}=\frac{2}{3}\\x-\frac{3}{10}=-\frac{2}{3}\end{cases}}\Rightarrow\orbr{\begin{cases}x=\frac{2}{3}+\frac{3}{10}\\x=\left(-\frac{2}{3}\right)+\frac{3}{10}\end{cases}}\Rightarrow\orbr{\begin{cases}x=\frac{29}{30}\\x=-\frac{11}{30}\end{cases}}\)

Vậy \(x\in\left\{\frac{29}{30};-\frac{11}{30}\right\}.\)

Chúc bạn học tốt!

\(\left(x-0,3\right)^2=0,\left(4\right)\)

\(\left(x-0,3\right)^2=\frac{4}{9}\)

\(\Rightarrow\left(x-0,3\right)^2=\left(\frac{2}{3}\right)^2\) hoặc  \(\left(x-0,3\right)^2=\left(\frac{-2}{3}\right)^2\)

\(\Rightarrow x-0,3=\frac{2}{3}\)                 hoặc   \(x-0,3=\frac{-2}{3}\)           

     \(x=\frac{2}{3}-0,3\)                             \(x=\frac{-2}{3}-0,3\)

     \(x=\frac{11}{30}\)                                        \(x=\frac{-29}{30}\)

                          Vậy \(x\in\left\{\frac{11}{30};\frac{-29}{30}\right\}\)

29-x/21 + 27-x/23 + 25-x/25 + 23-x/27 + 21-x/29 = -5

1 + 29-x/21 + 1 + 27-x/23 + 1 + 25-x/25 + 1 + 23-x/27 + 1 + 21-x/29 = 0 

50-x/21 + 50-x/23 + 50-x/25 + 50-x/27 + 50-x/29 = 0

(50-x) (1/21 + 1/23 + 1/25 + 1/27 + 1/29) = 0

Vì: 1/21 + 1/23 + 1/25 + 1/27 + 1/2 > 0

=> 50 - x = 0

             x = 50

Vậy x = 50

\(\frac{-1}{3}+\frac{0,2-0,3+\frac{5}{11}}{-0,3+\frac{9}{16}-\frac{15}{12}}\)

\(=\frac{-1}{3}+\frac{\frac{2}{10}-\frac{3}{10}+\frac{5}{11}}{\frac{-3}{10}+\frac{9}{16}-\frac{15}{12}}\)

\(=\frac{-1}{3}+\frac{\frac{39}{110}}{\frac{-79}{80}}\)

\(=\frac{-1}{3}-\frac{312}{869}\)

\(=\frac{-1805}{2607}\)

tự làm là hạnh phúc của mỗi công dân.

p toán 5 ko