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

[ 6-A114 - op net sinds 3.10.13-(E)-5.4.2026 ]

Translation in   E N G L I S H

\(\displaystyle\lim_{x\to\,0}\:(\cos x)^\frac{1}{x^2}\:=\) A.   \(1\)
B.   \(e\)
C.   \(\frac{1}{e}\)
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
Dit levert :
       \(\large\displaystyle\lim_{x\to 0}\:(\cos x)^{\frac{1}{x^2}}\:=\displaystyle\lim_{x\to 0}\:e^{\frac{\ln\cos x}{x^2}}\)
We gaan nu de limiet zoeken van de exponent (grondtal e is constant).
\(\displaystyle\lim_{x\to\,0}\:\frac{\ln\cos x}{x^2}\left(=\frac00\right)\overset{H}{=}\lim_{x\to}\:\frac{\frac{1}{\cos x}(-\sin x)}{2x}=-\frac12\lim_{x\to0}\:\frac{\tan x}{x}=-\frac 12\)
\(\text{Bijgevolg is}\quad\displaystyle\lim_{x\to 0}\:(\cos x)^\frac{1}{x^2}=e^{-\frac12}=\frac{1}{\sqrt e}\;(\approx 0,6)\)
gricha - vA114 - 3.10.13
gricha