Đáp án + Giải thích các bước giải:
18)
`3/5-1/5|x-1/2|=25%`
`=>3/5-1/5|x-1/2|=1/4`
`=>1/5|x-1/2|=3/5-1/4`
`=>1/5|x-1/2|=12/20-5/20`
`=>1/5|x-1/2|=7/20`
`=>|x-1/2|=7/20:1/5`
`=>|x-1/2|=7/20*5`
`=>|x-1/2|=7/4`
`=>` \(\left[ \begin{array}{l}x-\frac{1}{2}=\frac{7}{4}\\x-\frac{1}{2}=\frac{-7}{4}\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=\frac{7}{4}+\frac{1}{2}\\x=\frac{-7}{4}+\frac{1}{2}\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=\frac{7}{4}+\frac{2}{4}\\x=\frac{-7}{4}+\frac{2}{4}\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=\frac{9}{4}\\x=\frac{-5}{4}\end{array} \right.\)
Chọn `B`
19)
`(x-1)/4=16/(x-1)`
`=>(x-1).(x-1)=16.4`
`=>(x-1)^2=64`
`=>` \(\left[ \begin{array}{l}x-1=8\\x-1=-8\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=8+1\\x=-8+1\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=9\\x=-7\end{array} \right.\)
Chọn `C`
