giúp mik vs A: 4/7.x-1/5=2/3 B:7/9-5/9:x=1/6 C:|-2/5x+1/5| – 1/4

Đáp án:

Giải thích các bước giải:

`a)4/7.x-1/5=2/3`

`⇒4/7x=2/3+1/5`

`⇒4/7x={13}/{15}`

`⇒x={13}/{15}:4/7`

`⇒x={91}/{60}`

Vậy `x={91}/{60}`

`b)7/9-5/9:x=1/6`

`⇒5/9:x=7/9-1/6`

`⇒5/9:x={11}/{18}`

`⇒x=5/9:{11}/{18}`

`⇒x={10}/{11}`

Vậy `x={10}/{11}`

`c) |-2/5x+1/5| – 1/4=3/4`

`⇒|-2/5x+1/5| =3/4+1/4`

`⇒|-2/5x+1/5| =1`

`⇒`\(\left[ \begin{array}{l}-\frac{2}{5}x+\frac{1}{5}=1\\-\frac{2}{5}x+\frac{1}{5}=-1\end{array} \right.\)

`⇒`\(\left[ \begin{array}{l}-\frac{2}{5}x=1-\frac{1}{5}\\-\frac{2}{5}x=-1-\frac{1}{5}\end{array} \right.\)

`⇒`\(\left[ \begin{array}{l}-\frac{2}{5}x=\frac{4}{5}\\-\frac{2}{5}x=\frac{-6}{5}\end{array} \right.\)

`⇒`\(\left[ \begin{array}{l}x=\frac{4}{5}:(-\frac{2}{5})\\x=\frac{-6}{5}:(-\frac{2}{5})\end{array} \right.\)

`⇒`\(\left[ \begin{array}{l}x=-2\\x=3\end{array} \right.\) 

Vậy `x∈{-2;3}`