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Calculer \[\lim_{x\rightarrow 0}\ \ \frac{\cos (x^4)-1}{x^4e^x} ;\]
\[\lim_{x\rightarrow 0}\ \ \frac{\ln{\cos ax}}{\ln {\cos bx}} ;\]
\[\lim_{x\rightarrow 0}\ \ x^2\left( \exp \frac{1}{x} - \exp\frac{1}{x+1} \right).\]
Calculer \[\lim_{x\rightarrow 0}\ \ \frac{\cos (x^4)-1}{x^4e^x} ;\]
\[\lim_{x\rightarrow 0}\ \ \frac{\ln{\cos ax}}{\ln {\cos bx}} ;\]
\[\lim_{x\rightarrow 0}\ \ x^2\left( \exp \frac{1}{x} - \exp\frac{1}{x+1} \right).\]