$$\int \frac{dx}{x\sqrt{x^2 - a^2}}$$ is

A

$$\frac{1}{a}\cosec^{-1}\left(\frac{x}{a}\right)$$

B

$$\frac{1}{a}\sin^{-1}\left(\frac{x}{a}\right)$$

C

$$\frac{1}{a}\cos^{-1}\left(\frac{x}{a}\right)$$

D

$$\frac{1}{a}\sec^{-1}\left(\frac{x}{a}\right)$$