적분 $\displaystyle \int _ {1/2} ^ {1} {} (\arccos x) ^ {2} dx$ 를 구하면?

• ①$\displaystyle \frac{\pi} {6} -2+ \sqrt {3} - \frac{\pi ^ {2}} {72}$
• ②$\displaystyle \frac{\pi} {6} +2+ \sqrt {3} - \frac{\pi ^ {2}} {72}$
• ③$\displaystyle \frac{\sqrt {3} \pi} {3} +1- \frac{\pi ^ {2}} {18}$
• ④$\displaystyle \frac{\sqrt {3} \pi} {3} -1- \frac{\pi ^ {2}} {18}$
• ⑤$\displaystyle \frac{\sqrt {3} \pi} {3} -1+ \frac{\pi ^ {2}} {18}$