Comment 2 for bug 817709

Thank you for your bug report and taking the time to make Ubuntu better.

I do actually think everything you need is already there: For converting degrees to radians you can use the general conversion mechanism present in the "advanced" mode -- In the box in the type left chose "Angles" -> "degrees" and in the one on the right chose "radians".
Pi is also there, try the "π" button (also in "advanced" mode, above "=") or use Ctrl+P
For arctan: The documentation says you can use "atan" but that apparently does not work. What does work however is using tan-¹ by typing "tan" and then pressing Ctrl+I for inversion.

I've mark the bug as invalid, please feel free to reopen it if you still think it should be filed as a bug.