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}`
