Đáp án:
\(\begin{array}{l}
d)\left[ \begin{array}{l}
D = - 8\\
D = - 2
\end{array} \right.\\
e)\left[ \begin{array}{l}
E = - 36\\
E = 36
\end{array} \right.\\
f)\left[ \begin{array}{l}
F = 31\\
F = 33
\end{array} \right.
\end{array}\)
Giải thích các bước giải:
\(\begin{array}{l}
d)D = 15{x^3} - 6x - 35{x^2} - 15{x^3} - 5 + 35{x^2}\\
= - 6x - 5\\
Thay:\left| x \right| = \dfrac{1}{2} \to \left[ \begin{array}{l}
x = \dfrac{1}{2}\\
x = - \dfrac{1}{2}
\end{array} \right.\\
\to \left[ \begin{array}{l}
D = - 6.\dfrac{1}{2} - 5\\
D = - 6.\left( { - \dfrac{1}{2}} \right) - 5
\end{array} \right.\\
\to \left[ \begin{array}{l}
D = - 8\\
D = - 2
\end{array} \right.\\
e)E = 15{x^3} - 12x + 8{x^2} - 15{x^3} - 8{x^2}\\
= - 12x\\
Thay:\left| x \right| = 3 \to \left[ \begin{array}{l}
x = 3\\
x = - 3
\end{array} \right.\\
\to \left[ \begin{array}{l}
E = - 12.3\\
E = - 12.\left( { - 3} \right)
\end{array} \right.\\
\to \left[ \begin{array}{l}
E = - 36\\
E = 36
\end{array} \right.\\
f)F = {x^5} - {x^3}{y^2} + {x^3}{y^2} - {y^3}\\
= {x^5} - {y^3}\\
Thay:x = 2;\left| y \right| = 1 \to \left[ \begin{array}{l}
x = 2;y = 1\\
x = 2;y = - 1
\end{array} \right.\\
\to \left[ \begin{array}{l}
F = {2^5} - {1^3}\\
F = {2^5} - {\left( { - 1} \right)^3}
\end{array} \right. \to \left[ \begin{array}{l}
F = 31\\
F = 33
\end{array} \right.
\end{array}\)
