Đáp án:
\[\begin{array}{l}
B = 0\\
P = 75\\
Q = - 97,75
\end{array}\]
Giải thích các bước giải:
Ta có:
\(\begin{array}{l}
B = x\left( {x - y + 1} \right) - y\left( {y + 1 - x} \right)\\
\Leftrightarrow B = {x^2} - xy + x - {y^2} - y + xy\\
\Leftrightarrow B = {x^2} + x - {y^2} - y\\
\Leftrightarrow B = \left( {x - y} \right)\left( {x + y} \right) + \left( {x - y} \right)\\
\Leftrightarrow B = \left( {x - y} \right)\left( {x + y + 1} \right)\\
x = \frac{{ - 2}}{3};y = \frac{{ - 1}}{3} \Rightarrow x + y + 1 = 0 \Rightarrow B = 0
\end{array}\)
\(\begin{array}{l}
P = 5x\left( {{x^2} - 3} \right) + {x^2}\left( {7 - 5x} \right) - 7{x^2}\\
\Leftrightarrow P = 5{x^3} - 15x + 7{x^2} - 5{x^3} - 7{x^2}\\
\Leftrightarrow P = - 15x\\
x = - 5 \Rightarrow P = 75
\end{array}\)
\(\begin{array}{l}
Q = x\left( {x - y} \right) + y\left( {x - y} \right) = \left( {x - y} \right)\left( {x + y} \right)\\
\left\{ \begin{array}{l}
x = 1,5\\
y = 10
\end{array} \right. \Rightarrow Q = \left( {1,5 - 10} \right)\left( {1,5 + 10} \right) = - 97,75
\end{array}\)
