Đáp án:
$\begin{array}{l}
- x.\left( { - 3x + \frac{1}{2}} \right) + \left( {6x - 1} \right).\left( {2.\frac{1}{2}x} \right)\\
= x.\left( {3x - \frac{1}{2}} \right) + \left( {6x - 1} \right).x\\
= x.\left( {3x - \frac{1}{2} + 6x - 1} \right)\\
= x.\left( {9x - \frac{3}{2}} \right)\\
= 9{x^2} - \frac{3}{2}x
\end{array}$