Đáp án:
$\begin{array}{l}
1)B = - {x^2} + 2xy + {y^2}\\
Khi:x = 0,5;y = 2\\
\Rightarrow B = - {\left( {0,5} \right)^2} + 2.0,5.2 + {2^2}\\
= - 0,25 + 2 + 4\\
= 5,75\\
2){x^2}{y^2} + xy\\
Khi:x = 1;y = ??\\
3)\\
a)3{m^3} - {m^2} + 1\\
+ Khi:m = - 2\\
\Rightarrow 3.{\left( { - 2} \right)^3} - {\left( { - 2} \right)^2} + 1\\
= 3.\left( { - 8} \right) - 4 + 1\\
= - 24 - 4 + 1\\
= - 27\\
+ Khi:m = 3\\
\Rightarrow {3.3^3} - {3^2} + 1\\
= 81 - 9 + 1\\
= 73\\
b) - {m^2} + 3\\
+ Khi:m = - 2\\
\Rightarrow - {\left( { - 2} \right)^2} + 3 = - 4 + 3 = - 1\\
+ Khi:m = 3\\
\Rightarrow - {3^2} + 3 = - 9 + 3 = - 6\\
B4)\\
a)CD = 5 + 2 = 7\\
\Rightarrow Chu\,vi:2.\left( {5 + 7} \right) = 2.12 = 24\left( m \right)\\
b)CR = x - 3\left( m \right)\\
\Rightarrow S = x.\left( {x - 3} \right)\left( {{m^2}} \right)
\end{array}$