TH1: \(\left|x+1\right|=x+1\) khi \(x\ge-1\)
\(\Rightarrow\)\(3x^2+2\left(x+1\right)=3\)
\(\Leftrightarrow3x^2+2x+2-3=0\)
\(\Leftrightarrow3x^2+2x-1=0\)
\(\Leftrightarrow3x^2+3x-x-1=0\)
\(\Leftrightarrow3x\left(x+1\right)-\left(x+1\right)=0\)
\(\Leftrightarrow\left(x+1\right)\left(3x-1\right)=0\)
\(\Leftrightarrow\left\{{}\begin{matrix}x+1=0\\3x-1=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-1\\x=\dfrac{1}{3}\end{matrix}\right.\)
TH2: \(\left|x+1\right|=-x-1\) khi \(x\le-1\)
\(\Rightarrow3x^2+2\left(-x-1\right)=3\)
\(\Leftrightarrow3x^2-2x-2-3=0\)
\(\Leftrightarrow3x^2-2x-5=0\)
\(\Leftrightarrow3x^2+3x-5x-5=0\)
\(\Leftrightarrow3x\left(x+1\right)-5\left(x+1\right)=0\)
\(\Leftrightarrow\left(x+1\right)\left(3x-5\right)=0\)
\(\Leftrightarrow\left\{{}\begin{matrix}x+1=0\\3x-5=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-1\\x=\dfrac{5}{3}\end{matrix}\right.\)
Vậy===--
=.= hok tốt!!
