Đáp án:
$\begin{array}{l}
A = 2x\left( {3{x^2} + 5} \right) - x\left( {3x - {x^2}} \right) - {x^2}\\
= 6{x^3} + 10x - 3{x^2} + {x^3} - {x^2}\\
= 7{x^3} - 4{x^2} + 10x\\
= {7.2^3} - {4.2^2} + 10.2\\
= 56 - 16 + 20 = 60\\
b)B = \left( {x - y} \right)\left( {{x^2} - xy} \right) - x\left( {{x^2} + 2{y^2}} \right)\\
= x{\left( {x - y} \right)^2} - x.\left( {{x^2} + 2{y^2}} \right)\\
= x\left( {{x^2} - 2xy + {y^2} - {x^2} - 2{y^2}} \right)\\
= x\left( { - 2xy - {y^2}} \right)\\
= - xy\left( {2x + y} \right)\\
= - 2.\left( { - 3} \right).\left( {2.2 - 3} \right)\\
= 6\\
c)C = 6\left( {{x^2} - x} \right) - {x^2}\left( {4x - 2} \right) + 4x\left( {{x^2} - 2x + 3} \right)\\
= 6{x^2} - 6x - 4{x^3} + 2{x^2} + 4{x^3} - 8{x^2} + 12x\\
= 6x\\
= 6.\left( { - 4} \right)\\
= - 24\\
d)D = x\left( {{x^2} + xy + {y^2}} \right) - y\left( {{x^2} + xy + {y^2}} \right)\\
= \left( {x - y} \right)\left( {{x^2} + xy + {y^2}} \right)\\
= {x^3} - {y^3}\\
= {5^3} - {\left( { - 1} \right)^3}\\
= 126
\end{array}$
