exo7 730

Calculer $$\lim_{x\rightarrow 0}\ \ \frac{\cos (x^4)-1}{x^4e^x} ;$$

$$\lim_{x\rightarrow 0}\ \ \frac{\ln{\cos ax}}{\ln {\cos bx}} ;$$

$$\lim_{x\rightarrow 0}\ \ x^2\left( \exp \frac{1}{x} - \exp\frac{1}{x+1} \right).$$