3x.(x+1)–6x–6=0
=>3$x^{2}$ +3x-6x-6=0
=>3$x^{2}$ -3x-6=0
=> 3($x^{2}$-x-2)=0
=>$x^{2}$-x-2=0
=>($x^{2}$-2.x.$\frac{1}{2}$+$\frac{1}{4}$ )-$\frac{9}{4}$ 0
=>$(x-\frac{1}{2} )^{2}$ =$\frac{9}{4}$=$(\frac{3}{2})^{2}$
=>x-$\frac{1}{2}$ =$\frac{3}{2}$ hoặc x-$\frac{1}{2}$ =-$\frac{3}{2}$
=>x=$\frac{3}{2}$+$\frac{1}{2}$hoặc x =-$\frac{3}{2}$+ $\frac{1}{2}$
=>x=2 hoặc x=-1
