Câu 1: a) (42-98)-(42-12)-12
=42-98-42+12-12=(42-42)-98+(12-12)=-98
b) (-5).4.(-2).3.(-25)
=(-5.-2).(4.-25).3=10.(-100).3=-3000
Câu 2:
a) x-105:3=-23
x-35=-23
x=(-23)+35
x=12
b)|x-8|+12=25
|x-8|=25-12
|x-8|=13
Th1:x-8=13
<=>x=13+8
<=>x=21
Th2:x-8=-13
<=>x=(-13)+8
<=>x=-5
Vậy x€{21;-5}