Giải thích các bước giải:
B1:
Ta có:
$\begin{array}{l}
y = \cos \sqrt {{x^3} + {x^2} + 2} \\
= - \sin \sqrt {{x^3} + {x^2} + 2} .\dfrac{{3{x^2} + 2x}}{{2\sqrt {{x^3} + {x^2} + 2} }}\\
= - \dfrac{{\left( {3{x^2} + 2x} \right)\sin \sqrt {{x^3} + {x^2} + 2} }}{{2\sqrt {{x^3} + {x^2} + 2} }}
\end{array}$
B2:
a) Ta có:
$\begin{array}{l}
\left\{ \begin{array}{l}
S \in \left( {SAC} \right);S \in \left( {SBD} \right)\\
O \in AC \subset \left( {SAC} \right);O \in BD \subset \left( {SBD} \right)
\end{array} \right.\\
\Rightarrow \left( {SAC} \right) \cap \left( {SBD} \right) = SO
\end{array}$
b) Ta có:
$\begin{array}{l}
\left\{ \begin{array}{l}
M \in SA;N \in SB\\
\dfrac{{SM}}{{MA}} = \dfrac{{SN}}{{NB}} = 2
\end{array} \right.\\
\Rightarrow MN//AB
\end{array}$
$\to MN//(ABCD)$
