a)
\(3x^2-2x-1=0\Leftrightarrow\left(3x^2-3x\right)+\left(x-1\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left(3x+1\right)=0\Leftrightarrow\left[{}\begin{matrix}x=1\\x=\dfrac{-1}{3}\end{matrix}\right.\)
b)
\(\Leftrightarrow\left(x^4-x^2\right)+\left(4x^2+4\right)=0\)
\(\Leftrightarrow x^2\left(x^2-1\right)-4\left(x^2-1\right)=\left(x^2-1\right)\left(x^2-4\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x^2-1=0\\x^2-4=0\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=-1\\x=1\\x=-2\\x=2\end{matrix}\right.\)
