Đáp án + Giải thích các bước giải:
`a)` `ĐK:-2x>=0=>x≤0`
`|7x+5|=x-3x`
`=>|7x+5|=-2x`
`=>` \(\left[ \begin{array}{l}7x+5=-2x\\7x+5=2x\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}7x+2x=-5\\7x-2x=-5\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}9x=-5\\5x=-5\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=-\dfrac{5}{9}\ (tmđk)\\x=-1\ (tmđk)\end{array} \right.\)
Vậy `x∈{-(5)/(9);-1}`
`b)` `ĐK:12-5x>=0=>x≤(12)/(5)`
`|7x+5|=12-5x`
`=>` \(\left[ \begin{array}{l}7x+5=12-5x\\7x+5=5x-12\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}7x+5x=12-5\\7x-5x=-12-5\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}12x=7\\2x=-17\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=\dfrac{7}{12}\ (tmđk)\\x=-\dfrac{17}{2}\ (tmđk)\end{array} \right.\)
Vậy `x∈{(7)/(12);-(17)/(2)}`
