\(a.\dfrac{4}{5}+x=\dfrac{8}{10}\\ \Rightarrow x=\dfrac{8}{10}-\dfrac{4}{5}\\ \Rightarrow x=\dfrac{8}{10}-\dfrac{8}{10}\\ \Rightarrow x=0\\ b.\dfrac{1}{7}-7\left(\dfrac{2}{3}-x\right)=-\dfrac{4}{7}\\ \Rightarrow\dfrac{1}{7}-\dfrac{14}{3}+7x=-\dfrac{4}{7}\\ \Rightarrow-\dfrac{95}{21}+7x=-\dfrac{4}{7}\\\Rightarrow7x=\dfrac{83}{21}\\ \Rightarrow x=\dfrac{83}{147} \)
`a)4/5+x=8/10`
`=>x=8/10-4/5`
`=>x=4/5-4/5`
`=>x=0`
Vậy `x=0`
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`b)1/7-7(2/3-x)=-4/7`
`=>7(2/3-x)=1/7-(-4/7)`
`=>7(2/3-x)=1/7+4/7`
`=>7(2/3-x)=5/7`
`=>2/3-x=5/7:7`
`=>2/3-x=5/7xx1/7`
`=>2/3-x=5/49`
`=>x=2/3-5/49`
`=>x=98/147-15/147`
`=>x=83/147`
Vậy `x=83/147`
