\(\Rightarrow\)X*(3/5+2/7)=31/70

\(\Rightarrow\)X*31/35=31/70

\(\Rightarrow\)X=31/70:31/35

\(\Rightarrow\)X=1/2

\(x.\frac{3}{5}+x.\frac{2}{7}=\frac{31}{70}\)

\(x.\frac{31}{35}=\frac{31}{70}\)

\(x=\frac{1}{2}\)

Bài 1: 

Ta có: \(x-35\%\cdot x=\dfrac{1}{25}\)

\(\Leftrightarrow65\%\cdot x=\dfrac{1}{25}\)

\(\Leftrightarrow x=\dfrac{1}{25}:\dfrac{13}{20}=\dfrac{1}{25}\cdot\dfrac{20}{13}=\dfrac{4}{65}\)

Vậy: \(x=\dfrac{4}{65}\)

Bài 2: 

a) Ta có: \(17\dfrac{2}{31}-\left(\dfrac{15}{17}+6\dfrac{2}{31}\right)\)

\(=17\dfrac{2}{31}-\dfrac{15}{17}-6\dfrac{2}{31}\)

\(=11+\dfrac{2}{31}-\dfrac{15}{17}\)

\(=\dfrac{5366}{527}\)

X x 3/5+ Xx 3/7=31/70

=>X x (3/5+3/7)=31/70

=>X x 36/35=31/70

=>X=31/70:36/35

=>X=31/72

X x 3/5+ Xx 3/7=31/70

=>X x (3/5+3/7)=31/70

=>X x 36/35=31/70

=>X=31/70:36/35

=>X=31/72

X x 3/5+ Xx 3/7=31/70

=>X x (3/5+3/7)=31/70

=>X x 36/35=31/70

=>X=31/70:36/35

=>X=31/72

\(\frac{7}{3}\)\(+\frac{1}{2}\)\(+\frac{-3}{70}\)\(=\frac{293}{105}\)
\(\frac{5}{12}\)\(+\frac{3}{-16}\)\(+\frac{3}{4}\)\(=\frac{47}{48}\)
\(\frac{5}{3}\)\(+\left(7+\frac{-5}{3}\right)=\frac{5}{3}\)\(+\frac{-5}{3}\)\(+7=0+7=7\)
\(\frac{-7}{31}\)\(+\left(\frac{24}{17}+\frac{7}{31}\right)=\left(\frac{-7}{31}+\frac{7}{31}\right)+\frac{24}{17}=0+\frac{24}{17}\)\(=\frac{24}{17}\)
\(\frac{3}{7}\)\(+\left(\frac{-1}{5}+\frac{-3}{7}\right)=\left(\frac{3}{7}+\frac{-3}{7}\right)+\frac{-1}{5}\)\(=0+\frac{-1}{5}\)\(=\frac{-1}{5}\)
Nếu được cho mình xin 1 k đúng ^_^

\(y\times\frac{3}{5}+y\times\frac{2}{7}=\frac{31}{70}\)

\(\Leftrightarrow y\times\left(\frac{3}{5}+\frac{2}{7}\right)=\frac{31}{70}\)

\(\Leftrightarrow y\times\frac{31}{35}=\frac{31}{70}\)

\(\Leftrightarrow y=\frac{1}{2}\)

y x \(\frac{3}{5}\)+ y x \(\frac{2}{7}\)= \(\frac{31}{70}\)

y x \(\left(\frac{3}{5}+\frac{2}{7}\right)\)= \(\frac{31}{70}\)

y x            \(\frac{31}{35}\)   =   \(\frac{31}{70}\)

y                             =      \(\frac{31}{70}\):  \(\frac{31}{35}\)

y                             =                \(\frac{1}{2}\)

Biểu thức  x x - 3 - x 2 + 3 x 2 x + 3 . x + 3 x 2 - 3 x - x x 2 - 9 xác định khi x – 3  ≠  0,2x + 3  ≠  0, x 2 - 3 x   ≠  0 và x 2 - 9   ≠  0

Suy ra: x  ≠  3; x  ≠  - 3/2 ; x  ≠  0; x  ≠  3 và x  ≠   ± 3

Với điều kiện x  ≠  3; x  ≠  - 3/2 ; x  ≠  0; x  ≠  - 3, ta có:

Vậy giá trị của biểu thức  x x - 3 - x 2 + 3 x 2 x + 3 . x + 3 x 2 - 3 x - x x 2 - 9 bằng 1 khi x  ≠  3; x  ≠  - 3/2 ; x  ≠  0; x  ≠  - 3