Let's take the limit
$$\lim_{x \to 0^+}\left(\frac{\operatorname{asin}{\left(x \right)}}{x}\right)$$
Do replacement
$$u = \operatorname{asin}{\left(x \right)}$$
$$x = \sin{\left(u \right)}$$
we get
$$\lim_{x \to 0^+}\left(\frac{\operatorname{asin}{\left(x \right)}}{x}\right) = \lim_{u \to 0^+}\left(\frac{\operatorname{asin}{\left(\frac{\sin{\left(u \right)}}{1} \right)}}{1^{-1} \sin{\left(u \right)}}\right)$$
=
$$\lim_{u \to 0^+}\left(\frac{\operatorname{asin}{\left(\sin{\left(u \right)} \right)}}{\sin{\left(u \right)}}\right) = \lim_{u \to 0^+}\left(\frac{u}{\sin{\left(u \right)}}\right)$$
=
$$\lim_{u \to 0^+} \frac{1}{\frac{1}{u} \sin{\left(u \right)}}$$
/sin(u)\
= 1 / ( lim |------| )
u->0+\ u / The limit
$$\lim_{u \to 0^+}\left(\frac{\sin{\left(u \right)}}{u}\right)$$
is first remarkable limit, is equal to 1.
The final answer:
$$\lim_{x \to 0^+}\left(\frac{\operatorname{asin}{\left(x \right)}}{x}\right) = 1$$