\(1)\) Để m có 2 nghiệm phân biệt thì \(\Delta>0\)
\(\Leftrightarrow\left[-2\left(m+1\right)\right]^2-4\left(m^2+3m+2\right)>0\)
\(\Leftrightarrow4\left(m+1\right)^2-4\left(m^2+3m+2\right)>0\)
\(\Leftrightarrow4\left(m^2+2m+1\right)-4\left(m^2+3m+2\right)>0\)
\(\Leftrightarrow4m^2+8m+4-4m^2-12m-8>0\)
\(\Leftrightarrow-4m-4>0\)
\(\Leftrightarrow-4m>4\)
\(\Leftrightarrow m< -1\)
\(2)\) Theo Vi-ét, ta có :
\(\left\{{}\begin{matrix}x_1+x_2=-\dfrac{b}{a}=2m+2\\x_1x_2=\dfrac{c}{a}=m^2+3m+2\end{matrix}\right.\)
Ta có :
\(x_1^2+x_2^2=12\)
\(\Leftrightarrow\left(x_1+x_2\right)^2-2x_1x_2-12=0\)
\(\Leftrightarrow\left(2m+2\right)^2-2\left(m^2+3m+2\right)-12=0\)
\(\Leftrightarrow4m^2+8m+4-2m^2-6m-4-12=0\)
\(\Leftrightarrow2m^2+2m-12=0\)
\(\Leftrightarrow\left\{{}\begin{matrix}m=2\\m=-3\end{matrix}\right.\)
