Đáp án:
$\text{c) ($\dfrac{x}{7}$ + 1) : (-4) = $\dfrac{5}{28}$}$
$\text{=>($\dfrac{x}{7}$+1) = $\dfrac{5}{28}$ . (-4) }$
$\text{=> ($\dfrac{x}{7}$ + 1) = $\dfrac{-5}{7}$ }$
$\text{=>$\dfrac{x}{7}$ = $\dfrac{-5}{7}$ - 1}$
$\text{=>$\dfrac{x}{7}$ = $\dfrac{-12}{7}$ }$
$\text{=>x = $\dfrac{-12}{7}$ . 7 }$
$\text{=> x = -12}$
$\text{Vậy x= -12}$
$\text{d) l $\dfrac{1}{2}$x - $\dfrac{3}{4}$ l -1 = $\dfrac{9}{4}$}$
$\text{=> l $\dfrac{1}{2}$x - $\dfrac{3}{4}$ l = $\dfrac{9}{4}$ + 1}$
$\text{=> l$\dfrac{1}{2}$x - $\dfrac{3}{4}$l = $\dfrac{13}{4}$}$
Th1
$\text{$\dfrac{1}{2}$x - $\dfrac{3}{4}$ = $\dfrac{13}{4}$}$
$\text{=> $\dfrac{1}{2}$x = $\dfrac{13}{4}$ + $\dfrac{3}{4}$}$
$\text{=>$\dfrac{1}{2}$x = 4}$
$\text{=>x = 4 : $\dfrac{1}{2}$}$
$\text{=> x = 8}$
Th2
$\text{$\dfrac{1}{2}$x - $\dfrac{3}{4}$ = $\dfrac{-13}{4}$}$
$\text{=> $\dfrac{1}{2}$x = $\dfrac{-13}{4}$ + $\dfrac{3}{4}$}$
$\text{=> $\dfrac{1}{2}$x =$\dfrac{-5}{2}$}$
$\text{=> x= $\dfrac{-5}{2}$ : $\dfrac{1}{2}$}$
$\text{=> x = -5}$
$\text{Vậy x ∈ { 8 ; -5}}$
