곡선 $\displaystyle y = \frac{e ^ {2 x} + e ^ {-2 x}} {4} \left (0 \leq x \leq 1 \right)$ 의 길이는?

• ①$\displaystyle \frac{1} {4} \left (e ^ {2} - \frac{1} {e ^ {2}} \right)$
• ②$\displaystyle \frac{1} {4} \left (e - \frac{1} {e} \right)$
• ③$\displaystyle \frac{1} {2} \left (e - \frac{1} {e} \right)$
• ④$\displaystyle 4 \left (e + \frac{1} {e} \right)$
• ⑤$\displaystyle 4 \left (e ^ {2} + \frac{1} {e ^ {2}} \right)$