Đáp án:
\(\begin{array}{l}
B22:\\
a)A = - 1000000\\
b)B = 8125\\
c)C = 728\\
B23:\\
A = 4
\end{array}\)
Giải thích các bước giải:
\(\begin{array}{l}
B22:\\
a)A = {x^3} + 3.{x^2}.3 + 3.x{.3^2} + {3^3}\\
= {\left( {x + 3} \right)^3}\\
Thay:x = - 103\\
\to A = {\left( { - 103 + 3} \right)^3} = - 1000000\\
b)B = x\left( {{x^2} - 15x + 75} \right)\\
Thay:x = 25\\
\to B = 25\left( {{{25}^2} - 15.25 + 75} \right)\\
= 25.325 = 8125\\
c)C = \left( {x + 1} \right)\left( {x - 1} \right)\left( {{x^2} + x + 1} \right)\left( {{x^2} - x + 1} \right)\\
= \left( {{x^3} + 1} \right)\left( {{x^3} - 1} \right)\\
= {x^6} - 1\\
Thay:x = - 3\\
\to C = {\left( { - 3} \right)^6} - 1 = 728\\
B23:\\
A = 2\left( {x - y} \right)\left( {{x^2} + xy + {y^2}} \right) - 3\left( {{x^2} + 2xy + {y^2}} \right)\\
Thay:x - y = 2\\
\to A = 2.2\left( {{x^2} + xy + {y^2}} \right) - 3\left( {{x^2} + 2xy + {y^2}} \right)\\
= 4{x^2} + 4xy + 4{y^2} - 3{x^2} - 6xy - 3{y^2}\\
= {x^2} - 2xy + {y^2}\\
= {\left( {x - y} \right)^2}\\
= {2^2} = 4
\end{array}\)
