a) $-\dfrac{5}{12}:|-\dfrac{5}{6}:x|=-\dfrac{5}{9}$
$|-\dfrac{5}{6}:x|=-\dfrac{5}{12}:-\dfrac{5}{9}$
$|-\dfrac{5}{6}:x|=-\dfrac{5}{12}.-\dfrac{9}{5}=\dfrac{3}{4}$
⇒ TH1: $-\dfrac{5}{6}:x=\dfrac{3}{4}$
$x=-\dfrac{5}{6}:\dfrac{3}{4}=-\dfrac{5}{6}.\dfrac{4}{3}=-\dfrac{10}{9}$
⇒ TH2: $-\dfrac{5}{6}:x=-\dfrac{3}{4}$
$x=-\dfrac{5}{6}:-\dfrac{3}{4}=-\dfrac{5}{6}.-\dfrac{4}{3}=\dfrac{10}{9}$
Vậy $x=(-\dfrac{10}{9},\dfrac{10}{9})$
b) $|2x-3|=5-x$
⇒ TH1: $2x-3=5-x$
$(2x-3)-(5-x)=0$
$2x-3-5+x=0$
$(2x+x)+(-3-5)=0$
$3x-8=0$
$3x=8⇒x=\dfrac{8}{3}$
⇒ TH2: $2x-3=x-5$
$(2x-3)-(x-5)=0$
$2x-3-x+5=0$
$(2x-x)+(-3+5)=0$
$x+2=0⇒x=-2$
Vậy $x=(\dfrac{8}{3},-2)$
c) $|1-3x|=x-7$
⇒ TH1: $1-3x=x-7$
$(1-3x)-(x-7)=0$
$1-3x-x+7=0$
$(-3x-x)+(1+7)=0$
$-4x+8=0$
$-4x=-8⇒x=-8:(-4)=2$
⇒ TH2: $1-3x=7-x$
$(1-3x)-(7-x)=0$
$1-3x-7+x=0$
$(-3x+x)+(1-7)=0$
$-2x-6=0$
$-2x=6⇒x=6:(-2)=-3$
Vậy $x=(2,-3)$
