Đối với hàm số \(f\left( x \right) = {e^{\cos 2x}}\), ta có:
(A) \({f'\left( {\frac{\pi }{6}} \right) = {e^{\frac{{\sqrt 3 }}{2}}}}\)
(B) \({f'\left( {\frac{\pi }{6}} \right) - {e^{\frac{{\sqrt 3 }}{2}}}}\)
(C) \({f'\left( {\frac{\pi }{6}} \right) = \sqrt {3e} }\)
(D) \({f'\left( {\frac{\pi }{6}} \right) = - \sqrt {3e} }\)
\(\begin{array}{l}
f'\left( x \right) = - 2\sin 2x{e^{\cos 2x}}\\
f\left( {\frac{\pi }{6}} \right) = - 2\sin \frac{\pi }{3}.{e^{\cos \frac{\pi }{3}}}\\
= - \sqrt 3 .{e^{\frac{1}{2}}} = - \sqrt {3e}
\end{array}\)
Chọn (D).
-- Mod Toán 12
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