This is a simple question that I'm trying to understand.
if A and B are 3×3 and B=(b1, b2, b3), then AB=(Ab1+Ab2+Ab3)
I envisioned A and B to be like so: $$ A = \begin{bmatrix} * & * & * \\ * & * & * \\ * & * & * \\ \end{bmatrix} $$
$$ B = \begin{bmatrix} * & * & * \\ * & * & * \\ * & * & * \\ \end{bmatrix} $$
It was given to me that B=(b1, b2, b3). I'm assuming this is from the first row of the matrix.
The final answer of AB is supposed to be AB=(Ab1+Ab2+Ab3). This cannot be right because you cannot add the products Ab1, Ab2, and Ab3. Instead, it should be AB=(Ab1 Ab2 Ab3) right? Not sure if I explained this right.