`2x(x-1/7)=0`
`<=> [(2x=0),(x-1/7=0):}`
`<=> [(x=0),(x=1/7):}`
Vậy `x in {0;1/7}`
`3/4+1/4:x =2/5`
`<=> 1/4:x = 2/5 -3/4 = -7/20`
`<=> x= 1/4 : (-7/20) = -5/7`
Vậy `x=-5/7`
d) `2x(x-1/7)=0`
`=>` \(\left[{}\begin{matrix}2x=0\\x-\dfrac{1}{7}=0\end{matrix}\right.\)
`=>` \(\left[{}\begin{matrix}x=0\\x=\dfrac{1}{7}\end{matrix}\right.\)
e) `3/4+1/4:x=2/5`
`=> 1/4:x=2/5-3/4`
`=> 1/4:x=8/20-15/20`
`=> 1/4:x=-7/20`
`=> x=-5/7`
\(d.< =>\left[{}\begin{matrix}2x=0\\x-\dfrac{1}{7}=0\end{matrix}\right.< =>\left[{}\begin{matrix}x=0\\x=\dfrac{1}{7}\end{matrix}\right.\)
\(e.< =>\dfrac{3}{4}+\dfrac{x}{4}=\dfrac{2}{5}=>\dfrac{x}{4}=-\dfrac{7}{20}=>x=-1,4\)
\(d. 2x\left(x-\dfrac{1}{7}\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}2x=0\\x-\dfrac{1}{7}=0\end{matrix}\right.\) \(\Rightarrow
\left[{}\begin{matrix}x=0\\x=\dfrac{1}{7}\end{matrix}\right.\)
Vậy \(x\in\left\{0;\dfrac{1}{7}\right\}\)
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\(e.
\dfrac{3}{4}+\dfrac{1}{4}:
x=\dfrac{2}{5}\)
\(\dfrac{1}{4}: x=\dfrac{2}{5}-\dfrac{3}{4}\)
\(\dfrac{1}{4}: x=\dfrac{8}{20}-\dfrac{15}{20}\)
\(\dfrac{1}{4}: x=\dfrac{-7}{20}\)
\(x=\dfrac{1}{4}:\dfrac{-7}{20}\)
Vậy \(x=\dfrac{-5}{7}\)
