a/ -6x = 18 <=> x = $\frac{18}{-6}$ = -3
b/ Nếu x $\geq$ 0 thì:
<=> x- 10 =-3
<=> x = -3+10
<=> x=7
Nếu x < 0 thì:
-x-10=-3
<=>-x=7
<=> x=-7
c/ <=> 6x + 5 =17
<=> 6x = 12
<=> x = $\frac{12}{6}$ = 2
d/ <=> 2x + 12 = 3x - 21
<=> 2x - 3x = -21 -12
<=> -x = - 33
<=> x=33