$ sudo apt-get remove libcgal9 

Uninstall libcgal9 including dependent package

If you would like to remove libcgal9 and it's dependent packages which are no longer needed from Ubuntu,

$ sudo apt-get remove --auto-remove libcgal9 

Use Purging libcgal9

If you use with purge options to libcgal9 package all the configuration and dependent packages will be removed.

$ sudo apt-get purge libcgal9 

If you use purge options along with auto remove, will be removed everything regarding the package, It's really useful when you want to reinstall again.

$ sudo apt-get purge --auto-remove libcgal9 

See Also,