\(1,\Leftrightarrow x^3-3x^2+3x-1+3x^2+6x-x^3+8=16\\ \Leftrightarrow9x=9\\ \Leftrightarrow x=1\\ 2,\Leftrightarrow x^3+8-x^3-2x=15\\ \Leftrightarrow-2x=7\\ \Leftrightarrow x=-\dfrac{7}{2}\\ 3,\Leftrightarrow x\left(x^2-25\right)-\left(x^3+8\right)=3\\ \Leftrightarrow x^3-25x-x^3-8=3\\ \Leftrightarrow-25x=11\\ \Leftrightarrow x=-\dfrac{11}{25}\\ 4,làm.câu.trên.rùi\\ 5,\Leftrightarrow x^3+9x^2+27x+27-9x^3-6x^2-x+8x^3+1=28\\ \Leftrightarrow3x^2+26x=0\\ \Leftrightarrow x\left(3x-26\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\x=\dfrac{26}{3}\end{matrix}\right.\)
Bài 2:
\(\left(x+2\right)\left(x^2-2x+4\right)-x\left(x^2+2\right)=15\)
\(\Leftrightarrow x^3+8-x^3-2x=15\)
\(\Leftrightarrow8-2x=15\)
\(\Leftrightarrow2x=-7\)
\(\Leftrightarrow x=\dfrac{-7}{2}\)