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