Đáp án:
$\begin{array}{l}
6){\left( {x - 1} \right)^2} + {\left( {x + 5} \right)^2}\\
= {x^2} - 2x + 1 + {x^2} + 10x + 25\\
= 2{x^2} + 8x + 26\\
7)\\
- 4x{\left( {2x + 3} \right)^2} - \left( {2x - 1} \right)\left( {x + 3} \right)\left( {x - 3} \right)\\
= - 4x\left( {4{x^2} + 12x + 9} \right) - \left( {2x - 1} \right)\left( {{x^2} - 9} \right)\\
= - 16{x^3} - 48{x^2} - 36x\\
- \left( {2{x^3} - 18x - {x^2} + 9} \right)\\
= - 14{x^3} - 47{x^2} - 18x - 9\\
8)\\
- 2x\left( {3x + 2} \right)\left( {3x - 2} \right) + 5{\left( {x + 2} \right)^2}\\
= - 2x\left( {9{x^2} - 4} \right) + 5\left( {{x^2} + 4x + 4} \right)\\
= - 18{x^3} + 8x + 5{x^2} + 20x + 20\\
= - 18{x^3} + 5{x^2} + 28x + 20\\
9)\\
- \left( {x - 1} \right)\left( {2x - 1} \right)\left( {2x + 1} \right) + \left( {7x - 8} \right)\left( {7x + 8} \right)\\
= - \left( {x - 1} \right)\left( {4{x^2} - 1} \right) + 49{x^2} - 64\\
= - 4{x^3} + x + 4{x^2} - 1 + 49{x^2} - 64\\
= - 4{x^3} + 53{x^2} + x - 65\\
10)\\
- 10{\left( {2x + 3} \right)^2} + 5x{\left( {3x - 2} \right)^2} - 4x{\left( {x - 5} \right)^2}\\
= - 10\left( {4{x^2} + 12x + 9} \right) + 5x\left( {9{x^2} - 12x + 4} \right)\\
- 4x\left( {{x^2} - 10x + 25} \right)\\
= - 40{x^2} - 120x - 90 + 45{x^3} - 60{x^2} + 20x\\
- 4{x^3} + 40{x^2} - 100x\\
= 41{x^3} - 60{x^2} - 200x - 90
\end{array}$
