Question

compute if possible :B^T A^T

Answer 1

That's matrix multiplication. Transposes are just the matrix "flipped" along the down-right diagonal (aka "main diagonal"), then multiply.

Answer 2

Here's the linear algebra lecture with matrix multiplication: http://ocw.mit.edu/courses/mathematics/18-06sc-linear-algebra-fall-2011/ax-b-and-the-four-subspaces/multiplication-and-inverse-matrices/

Answer 3

thank you

Answer 4

No problem. That course has a lot of applications included, so if you have more questions that would be the first place I'd look if I were you.