Đáp án:
$\begin{array}{l}
10)\left( {5 - x} \right){x^2};\left( { - 5} \right):SAI\\
11)\text{Đơn thức là}:b)9{x^2}yz\\
12)\\
a)2,5{x^2}y \Rightarrow \left\{ \begin{array}{l}
\text{Hệ số}:2,5\\
\text{Biến}:{x^2}y
\end{array} \right.\\
b)0,25.{x^2}{y^2} \Rightarrow \left\{ \begin{array}{l}
\text{Hệ số}:0,25\\
\text{Biến}:{x^2}{y^2}
\end{array} \right.\\
b)x = 1;y = - 1\\
\Rightarrow 2,5{x^2}y = 2,{5.1^2}.\left( { - 1} \right) = - 2,5\\
\Rightarrow 0,25.{x^2}{y^2} = 0,25\\
13)\\
a) - \dfrac{1}{3}{x^2}y.2x{y^3}\\
= - \dfrac{1}{3}.2.{x^2}.x.y.{y^3}\\
= - \dfrac{2}{3}.{x^3}{y^4}\\
\Rightarrow \text{Bậc}:7\\
b)\dfrac{1}{4}{x^3}y.\left( { - 2{x^3}{y^5}} \right)\\
= - \dfrac{1}{2}{x^6}.{y^6}\\
\Rightarrow \text{Bậc}:12\\
14)x = - 1;y = 1\\
\Rightarrow \left\{ \begin{array}{l}
- 9xy\\
9{x^2}y\\
- 9x{y^2}\\
9{x^2}{y^2}
\end{array} \right.
\end{array}$
