Đáp án:
$\begin{array}{l}
1)\\
B\left( x \right) = 0\\
\Rightarrow x + 1 = 0\\
\Rightarrow x = - 1\\
b)\\
x = 2;y = 1\\
\Rightarrow A = x{y^2} + 3xy + 1\\
= {2.1^2} + 3.2.1 + 1\\
= 2 + 6 + 1 = 9\\
2)\\
P\left( x \right) = 2x + 4{x^2} - 5\\
= 4{x^2} + 2x - 5\\
Q\left( x \right) = 3 + 7{x^2} + x\\
= 7{x^2} + x + 3\\
\Rightarrow P\left( x \right) + Q\left( x \right)\\
= 4{x^2} + 2x - 5 + 7{x^2} + x + 3\\
= 11{x^2} + 3x - 2\\
P\left( x \right) - Q\left( x \right)\\
= 4{x^2} + 2x - 5 - \left( {7{x^2} + x + 3} \right)\\
= - 3{x^2} + x - 8
\end{array}$