Compute the following limits:

$($a$)$ lim x$+$ $(1+$ ax $+(2$a$)$x$))/(1$ ax $(3$a$)$x$)$ where $($i$)$ a $=0\mathrm{.}4($ii$)$ a $=0\mathrm{.}8,$

$($b$)$ lim x$+$$(1(1/2$x$))^3$x