Question

TÌm x:

\(7x^3+12x^2-4x=0\)

Answer 1

$7x^3+12x^2-4x=0$

\(\Rightarrow x\left(7x^2+12x-4\right)=0\)

\(\Rightarrow x\left(7x^2+14x-2x-4\right)=0\)

\(\Rightarrow x\left[7x\left(x+2\right)-2\left(x+2\right)\right]=0\)

\(\Rightarrow x\left(7x-2\right)\left(x+2\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}x=0\\7x-2=0\\x+2=0\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=0\\7x=0+2=2\\x=0-2=-2\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=0\\x=\dfrac{2}{7}\\x=-2\end{matrix}\right.\)

Vậy \(x\in\left\{0;\dfrac{2}{7};-2\right\}\)