\(\Leftrightarrow x^4-2x^3-2x^2+5x^3-10x^2-10x-2x^2+4x+4=0\\ \Leftrightarrow\left(x^2-2x-2\right)\left(x^2+5x-2\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x^2-2x-2=0\left(1\right)\\x^2+5x-2=0\left(2\right)\end{matrix}\right.\)
Ta có \(\Delta\left(1\right)=4+8=12;\Delta\left(2\right)=25+8=33\)
\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{2-2\sqrt{3}}{2}=1-\sqrt{3}\\x=\dfrac{2+2\sqrt{3}}{2}=1+\sqrt{3}\\x=\dfrac{-5+\sqrt{33}}{2}\\x=\dfrac{-5-\sqrt{33}}{2}\end{matrix}\right.\)
\(x^4+3x^3-14x^2-6x+4=0\\ \Leftrightarrow\left(x^4-2x^3-2x^2\right)+\left(5x^3-10x^2-10x\right)-\left(2x^2-4x-4\right)=0\\ \Leftrightarrow\left(x^2-2x-2\right)\left(x^2+5x-2\right)=0\\ \Leftrightarrow....\)
