1.1.2 Greatest hits from previous weeks

1.1.2.1 Can Mathematica do symbolic linear algebra?

http://mathematica.stackexchange.com/questions/3242/can-mathematica-do-symbolic-linear-algebra

 
For instance, is there some way I can say "let A and B be arbitrary real 
$m\times n$ and $k\times m$ matrices, 
Simplify[Transpose[Transpose[A].Transpose[B]]]" and Mathematica would 
simplify it to B.A? 
...
 

- asked by nikie (24 votes), answered by helen (12 votes)

1.1.2.2 How to force 2+2=5

http://mathematica.stackexchange.com/questions/48929/how-to-force-22-5

 
I was looking at this question (writing a program such that 2 + 2 = 5) 
and tried to write something in Mathematica, but I couldn't get 
something to work without completely replacing Plus. Neither of  ...
 

- asked by Artefacto (4 votes), answered by halirutan (7 votes)