The positive coterminal angle is obtained by adding 2π to the given angle, as follows:
[tex]\frac{11\pi}{6}+2\pi=(\frac{11}{6}+2)\pi=\frac{11+2\cdot6}{6}\pi=\frac{23}{6}\pi[/tex]The negative coterminal angle is obtained by subtracting 2π to the given angle, as follows
[tex]\frac{11\pi}{6}-2\pi=(\frac{11}{6}-2)\pi=\frac{11-2\cdot6}{6}\pi=-\frac{1}{6}\pi[/tex]