Đáp án:
$\begin{array}{l}
a)\sqrt x \left( {\sqrt x - 3} \right) - \left( {\sqrt x + 1} \right)\left( {2\sqrt x - 3} \right) + 5\sqrt x \left( {\sqrt x - 2} \right)\\
= x - 3\sqrt x - \left( {2x - 3\sqrt x + 2\sqrt x - 3} \right) + 5x - 10\sqrt x \\
= x - 3\sqrt x - 2x + \sqrt x + 3 + 5x - 10\sqrt x \\
= 4x - 12\sqrt x + 3\\
b)\left( {\sqrt x - 2} \right)\left( {\sqrt x - 1} \right) + \left( {\sqrt x + 3} \right)2\sqrt x - 3\sqrt x \left( {\sqrt x - 4} \right)\\
= x - 3\sqrt x + 2 + 2x + 6\sqrt x - 3x + 12\sqrt x \\
= 15\sqrt x + 2
\end{array}$