$\displaystyle \int _1^2 {{\frac{\sqrt {x^2 -1}} {x} dx}}$ 의 값은?

• ①$\displaystyle \sqrt 3 - \frac{\pi} {3}$
• ②$\displaystyle \sqrt 3 - \frac{\pi} {6}$
• ③$\displaystyle 2 \sqrt 3 - \frac{\pi} {3}$
• ④$\displaystyle 2 \sqrt 3 - \frac{\pi} {6}$