Đáp án:
$\begin{array}{l}
1)\\
x\left( {3x + 12} \right) - \left( {7x - 20} \right)\\
- {x^2}\left( {2x + 3} \right) + x\left( {2{x^2} - 5} \right)\\
= 3{x^2} + 12x - 7x + 20\\
- 2{x^3} - 3{x^2} + 2{x^3} - 5x\\
= 20\\
C2)\\
A = {x^5} - 70{x^4} - 70{x^3} - 70{x^2} - 70x + 34\\
= {x^5} - 71{x^4} + {x^4} - 71{x^3} + {x^3} - 71{x^2}\\
+ {x^2} - 71x + x + 34\\
= \left( {x - 71} \right)\left( {{x^4} + {x^3} + {x^2} + x} \right) + x + 34\\
= \left( {71 - 71} \right).\left( {{x^4} + {x^3} + {x^2} + x} \right) + 71 + 34\\
= 0.\left( {{x^4} + {x^3} + {x^2} + x} \right) + 105\\
= 105
\end{array}$