Tìm x biết :
a) |x|-2.|x+1|+3.|x+2|=0
b) 2.|x-3|+5x-1=0
c) |x+1|.|x+2|+|x+3|=4x
a) Nếu $x<-2\Rightarrow -x+2(x+1)-3(x+2)=0\Leftrightarrow x=-2$ (L)
Nếu $-2\leq x<-1\Rightarrow -x+2(x+1)+3(x+2)=0\Leftrightarrow x=-2$ (N)
Nếu $-1\leq x<0\Rightarrow -x-2(x+1)+3(x+2)=0\Leftrightarrow 0x=-4$ (L)
Nếu $x\geq 0\Rightarrow x-2(x+1)+3(x+2)=0\Leftrightarrow x=-2$ (L)
Vậy...
b) Nếu $x\geq 3\Rightarrow 2(x-3)+5x-1=0\Leftrightarrow x=1$ (L)
Nếu $x<3\Rightarrow 2(3-x)+5x-1=0\Leftrightarrow x=\dfrac{-5}3$ (N)
Vậy...
c) $4x=|x+1|+|x+2|+|x+3|\geq 0\Leftrightarrow x\geq 0$
$\Rightarrow x+1>0;x+2>0;x+3>0$
$\Rightarrow (x+1)(x+2)+x+3=4x$
$\Leftrightarrow \cdots$