another simple question



Thank you all! :)
One more simple question:

How can I do something like the "apart" operation in Mathematica?

(C1) a/c+b/d;

                                     b   a
(D1)                                 - + -
                                     d   C
(C2) rat(%);

                                   a d + b C
(D2)/R/                            ---------
                                      C d

Now given the form like [D2], how can I get something like D1?

I'm not good at Mathematics but I'm drawing a lot of people in my unversity to MAXIMA.  Formerly they don't even know this wonderful tool. They use Mathematica a lot.

They'll ask me a lot of questions like "How to do ... like that in Mathematica in MAXIMA?" I sometimes don't know. So I post the questions here. I wish you could help.

Thanks.

-- 
Wang Yin
DA Lab, Tsinghua University,
100084
Beijing China