PocketCAS is a free interface to the open-source Computer Algebra System giac/xcas.

xcas enables you to quickly solve complex algebraic problems, e.g. symbolic and numeric integration and derivation of non-trivial functions, solving differential equations etc. It has also a huge support for problems of linear algebra, like solving linear equation systems, multiplying and inverting matrices, finding eigenvalues (and eigenvectors, of course) and much more. If you do statistics or number theory, you will like xcas’ great functionality in those areas, too!

Changes:

Skin support: see Screenshots section for details.
For keyboard devices: Pressing Ctrl+Enter now starts the calculation, too.
After calculating, the keyboard will only hide if necessary. The results panel will scroll so that the bottom off the selected element is the same height as the top of the Keyboard.
Improved overall speed and snappiness.
Fixed: Memory leak when switching landscape/portrait mode. This is also a lot faster now.
Fixed: clicking image buttons now triggers as often as other buttons.

http://forum.xda-developers.com/showthread.php?t=415169