\(C=\left(x-1\right)\left(x+2\right)\left(x+3\right)\left(x+6\right)\\ C=\left(x^2+5x-6\right)\left(x^2+5x+6\right)\\ C=\left(x^2+5x\right)^2-36\ge-36\)
Dấu \("="\Leftrightarrow x^2+5x=0\Leftrightarrow\left[{}\begin{matrix}x=0\\x=-5\end{matrix}\right.\)


