A=|3x+1|-x-2 (1)
Ta có:|3x+1|=3x+1<=>3x+1 \(\ge\) 0<=>\(x\ge-\frac{1}{3}\)
|3x+1|=-(3x+1)<=>3x+1<0\(\Leftrightarrow x<-\frac{1}{3}\)
Nếu \(x\ge-\frac{1}{3}\) thì (1) trở thành : 3x+1-x-2=(3x-x)+(1-2)=2x-1
Nếu \(x<-\frac{1}{3}\) thì (1) trở thành :-(3x+1)-x-2=-3x-1-x-2=(-3x-x)+(-1-2)=-4x-3
Vậy..............