The method is basically the same The triangle in the circle is a right angled triangle. I also used z shapes and similar triangles.
Hmm.......I think I got it now
![Smiley :)](https://studentforums.biz/Smileys/default/smiley.gif)
Although it's quite hard to believe having a negative value for argument in the second quadrant. But I guess I never did a similar question previously. That's why I find it surprising
![Undecided :-\](https://studentforums.biz/Smileys/default/undecided.gif)
Thanks loads for your help
![Cheesy :D](https://studentforums.biz/Smileys/default/cheesy.gif)