Đáp án:
$\begin{array}{l}
a) - 4{x^5}\left( {{x^3} - 4{x^2} + 7x - 3} \right)\\
= - 4{x^8} + 16{x^7} - 28{x^6} + 12{x^5}\\
b) - 4x\left( {3x - 4} \right) + 7x\left( {x - 5} \right)\\
= - 12{x^2} + 16x + 7{x^2} - 35x\\
= - 5{x^2} - 19x\\
c)\left( {2x + 3y} \right)\left( {3x + 2y - 1} \right)\\
= 6{x^2} + 4xy - 2x + 9xy + 6{y^2} - 3y\\
= 6{x^2} + 6{y^2} - 2x - 3y + 13xy
\end{array}$
