Đáp án:
4C
Giải thích các bước giải:
\(\begin{array}{l}
C1:\\
x = - \dfrac{b}{{2a}} = - \dfrac{{ - 4}}{{2.1}} = 2\\
\to y = {2^2} - 4.2 - 5 = - 9\\
\to C\\
C2:\\
\left( {{x^2} - 1} \right)\left( {2 - x} \right) = 0\\
\to \left[ \begin{array}{l}
x = \pm 1\\
x = 2
\end{array} \right.\\
\to C\\
C3:\\
Xet:\\
y\left( { - x} \right) = {\left( { - x} \right)^2} - 2{\left( { - x} \right)^4}\\
= {x^2} - 2{x^4}\\
\to chan\\
\to B\\
C4:\\
2\overrightarrow b = \left( {2; - 4} \right)\\
Do:\overrightarrow a + 2\overrightarrow b \\
\to \left\{ \begin{array}{l}
3 + 2 = 5\\
4 - 4 = 0
\end{array} \right.\\
\to \overrightarrow a + 2\overrightarrow b = \left( {5;0} \right)\\
\to C\\
C5:\\
DK:\left\{ \begin{array}{l}
x + 3 \ne 0\\
x - 2 \ge 0
\end{array} \right.\\
\to x \ge 2
\end{array}\)
