Đáp án:
$\begin{array}{l}
a)A = 3{x^2}\left( {2y - 1} \right) - \left[ {2{x^2}\left( {5y - 3} \right) - \left( {x - 1} \right)2x} \right]\\
= 6{x^2}y - 3{x^2} - \left( {10{x^2}y - 6{x^2} - 2{x^2} + 2x} \right)\\
= 6{x^2}y - 3{x^2} - 10{x^2}y + 8{x^2} - 2x\\
= 5{x^2} - 2x - 4{x^2}y\\
b)\\
B = 4x\left( {2x - 3} \right) - 5x\left( {x - 2} \right)\\
= 8{x^2} - 12x - 5{x^2} + 10x\\
= 3{x^2} - 2x\\
= {3.2^2} - 2.2\left( {khi:x = 2} \right)\\
= 12 - 4\\
= 8\\
c)C = {\left( {x + 1} \right)^2} - {\left( {2 - {x^2}} \right)^2}\\
= {x^2} + 2x + 1 - \left( {{x^4} - 4{x^2} + 4} \right)\\
= {x^2} + 2x + 1 - {x^4} + 4{x^2} - 4\\
= - {x^4} + 5{x^2} + 2x - 3
\end{array}$
