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 \(x=1,875\)

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

Trả lời :

\(0,1+0,2+0,3+...+0,x=4,5\)

\(0,1\times1+0,1\times2+0,1\times3+...+0,1\times x=4,5\)

\(0,1\times\left(1+2+3+...+x\right)=4,5\)

\(1+2+3+...+x=4,5:0,1\)

\(1+2+3+...+x=45\)

\(\left(x+1\right)\times x:2=45\)

\(\left(x+1\right)\times x=45\times2\)

\(\left(x+1\right)\times x=90\)

Ta có : 90 = 9 x 10

Vậy x = 9