\(\displaystyle \lim_{x \to 0} \: (\cos x)^{\frac {1} {\sin^{{\small 2}} x}}\:=\) A.   \(1\)
B.   \(e\)
C.   \(\frac1e\)
D.   \(\sqrt e\)
E.   \(\frac{1}{\sqrt e}\)
A   B   C   D   E

[ 6-7485 - op net sinds 1.10.13-(E)-20.10.2026 ]

Translation in   E N G L I S H

\(\displaystyle \lim_{x \to 0} \: (\cos x)^{\frac {1} {\sin^{{\small 2}} x}}\:=\) A.   \(1\)
B.   \(e\)
C.   \(\frac1e\)
D.   \(\sqrt e\)
E.   \(\frac{1}{\sqrt e}\)

Oplossing - Solution

We houden rekening met de formule   a = eln a zodat ook bv. xx = ex.ln x
en dus ook :
        \(\displaystyle\lim_{x\to 0}\:(\cos x)^{\frac{1}{\sin^{{\small 2}}x}}\:=\displaystyle\lim_{x\to 0}\:e^{\frac{\ln\cos x}{\sin^2x}}\)
We gaan nu de limiet zoeken van de exponent (grondtal e is constant).
\(\displaystyle\lim_{x\to 0}\:\frac{\ln\cos x}{\sin^2x}\left(=\frac00\right)\overset{H}{=}\displaystyle\lim_{x\to 0}\:\frac{\frac{1}{\cos x}(-\sin x)}{2\sin x\cos x}\\=-\displaystyle\lim_{x\to 0}\:\frac{\sin x}{\cos x.2\sin x.\cos x}=-\displaystyle\lim_{x\to 0}\:\frac{1}{2\cos^2x}=-\frac{1}{2.1^2}=-\frac12\)
\(\text{Bijgevolg is}\quad\displaystyle\lim_{x\to 0}\:(\cos x)^{\frac{1}{\sin^{{\small 2}}x}}\:=e^{-\frac12}=\frac{1}{\sqrt e}\;(\approx 0,6)\) gricha - v7485 - 1.10.13

GWB