Bạn tham khảo nhé
a) 2.x - 15 = -21
<=> 2.x = -21 + 15
<=> 2.x = -6
<=> x = -3
Vậy x = -3
b) 12 - (30 - x) = -23
<=> 12 - 30 + x = -23
<=> -18 + x = -23
<=> x = -23 + 18
<=> x = -5
Vậy x = -5
c) x.(x - 3) = 0
<=> \(\left[ \begin{array}{l}x=0\\x-3=0\end{array} \right.\)
<=> \(\left[ \begin{array}{l}x=0\\x=3\end{array} \right.\)
Vậy \(\left[ \begin{array}{l}x=0\\x=3\end{array} \right.\)
d) ║x + 7║ - 2 = 0
<=> ║x + 7║ = 2 (1)
║x + 7║ = $\left \{ {{x+7 khix+7\geq 0 <=> x\geq-7} \atop {-x-7 khi x+7<0<=> x<-7}} \right.$
(1) <=> \(\left[ \begin{array}{l}\left \{ {{x\geq-7} \atop {x+7=2}} \right.\\\left \{ {{x<-7} \atop {-x-7=2}} \right.\end{array} \right.\)
<=> \(\left[ \begin{array}{l}\left \{ {{x\geq-7} \atop {x=-5(TM) }} \right.\\\left \{ {{x<-7} \atop {x=-9(TM)}} \right.\end{array} \right.\)
<=> \(\left[ \begin{array}{l}x=-5\\x=-9\end{array} \right.\)
Vậy \(\left[ \begin{array}{l}x=-5\\x=-9\end{array} \right.\)
