Question

Tìm x biết

(x-1)^3-(x+3)^3+28=0

Answer 1

\(\left(x-1\right)^3-\left(x+3\right)^3+28=0\)

\(\Leftrightarrow x^3-3x^2+3x-1-\left(x^3+9x^2+27x+27\right)+28=0\)

\(\Leftrightarrow x^3-3x^2+3x-1-x^3-9x^2-27x-27+28=0\)

\(\Leftrightarrow-12x^2-24x=0\Leftrightarrow-12x\left(x+2\right)=0\)

\(\Leftrightarrow\left\{{}\begin{matrix}-12x=0\\x+2=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=0\\x=-2\end{matrix}\right.\) vậy \(x=0;x=-2\)