Đáp án: -4
Giải thích các bước giải: $$x(x-1)(x+5)-(2x^2+1)(x+4,5)=3,5\\\Leftrightarrow x(x-1)(x+5)-(x+\frac{9}{2})(2x^2+1)=\frac{7}{2}\\\Leftrightarrow -x^3-5x^2-6x-\frac{9}{2}=\frac{7}{2}\\\Leftrightarrow -x^3-5x^2-6x-8=0\\\Leftrightarrow -(x+4)(x^2+x+2)=0\\\Leftrighatrrow (x+4)(x^2+x+2)=0\\\Leftrightarrow \left[\begin{array}{l}x+4=0\\x^2+x+2=0\end{array}\right.\\\Leftrightarrow x=-4\\x^2+x+2=0\end{array}\right.\\\Leftrightarrow \left[\begin{array}{l}x=-4\\x^2+x=-2\end{array}\right.\\\Leftrightarrow \left[\begin{array}{l}x=-4\\x^2+x+\frac{1}{4}=-\frac{7}{4}\end{array}\right.\\\Leftrightarrow \left[\begin{array}{l}x=-4\\(x+\frac{1}{2})^2=-\frac{7}{4}\end{array}\right.\\\Leftrighatrrow x=-4$$
