곡선 $\displaystyle y = \frac{x ^ {2}} {2} - \left (\frac{1} {4} \right) \ln x \left (1 \leq x \leq e \right)$ 의 길이는?

• ①$\displaystyle \frac{e ^ {2}} {4} + \frac{1} {4}$
• ②$\displaystyle \frac{e ^ {2}} {2} + \frac{1} {4}$
• ③$\displaystyle \frac{e ^ {2}} {4} - \left (\frac{1} {4} \right)$
• ④$\displaystyle \frac{e ^ {2}} {2} - \left (\frac{1} {4} \right)$