$\int {\frac{{dx}}{{\sqrt {{a^2}\, - \,{x^n}} \,}}\, = \,{{\sin }^{ - 1}}\,\frac{x}{a}} $
terms in a equation or terms having arithematic operations of addition and subtraction should have same dimensions.
$\Rightarrow \ln a^{2}-x^{n}$
$\operatorname{dim}\left(a^{2}\right)=\operatorname{dim}\left(x^{n}\right)$
$L^{2}=L^{n} \Rightarrow[n=2]$