a) $\lim _ x\rightarrow 0 \frac cosx-1 x ^ 2 $
$\lim _ x\rightarrow 0 \frac cosx-1 x ^ 2 =\frac1-10^2=\frac00$ Aplicamos L’Hôpital $\lim _ x\rightarrow 0 \frac cosx-1 x ^ 2 =\lim _ x\rightarrow 0 \frac-sen \:x2x=\frac00 \stackrelLH=\lim _ x\rightarrow 0\frac-cos \: (…)