곡선 $y^2 =x^3 (0 \leq y \leq 1)$ 의 길이는?

• ①$\displaystyle \frac{19} {27}$
• ②$\displaystyle \frac{10 \sqrt 10 -8} {27}$
• ③$\displaystyle \frac{11 \sqrt 11 -8} {27}$
• ④$\displaystyle \frac{12 \sqrt 12 -8} {27}$
• ⑤$\displaystyle \frac{13 \sqrt 13 -8} {27}$