$$\begin{gathered} 5{\mathrm{x}}^3 - 10{\mathrm{x}}^2 = 0 \\ <=> 5{\mathrm{x}}^2.\mathrm{x} - 5{\mathrm{x}}^2.2 = 0 <=> 5{\mathrm{x}}^2(\mathrm{x} - 2) = 0 \\ => \left(1\right): 5{\mathrm{x}}^2 = 0 => {\mathrm{x}}^2 = 0 => \mathrm{x} = 0 \\ => \left(2\right): \mathrm{x} - 2 = 0 => \mathrm{x} = 2 \end{gathered}$$   Bài đó nha

       x + x + 3 * x + 4 * x = 6723

<=> 2x + 3x + 4x = 6723   <=>    (2 + 3 + 4)x = 9x = 6723   <=>   x = 747