Description of problem:
The inverted trigonometric function do wrong calculation. All results I tested are shifted by something in significant points, like '1'. E.g. tan^-1 (1) gives me 50 i gcalctool, but correct result is 45, or sin^-1 (1) gives me 100, but the correct result is 90.

Version-Release number of selected component (if applicable):
gcalctool-6.4.2.1-1.fc17.i686

How reproducible:
100%

Steps to Reproduce:
1. Start gcalctool and switch to advanced mode
2. Click [tan], then [x^-1], [1] and press enter
3.
  
Actual results:
50

Expected results:
45

Additional info: