Question

0 -5
3 -2
If A=(-2 -1 5 9) and B=﹛4 0﹜
-6 1 ，
What is the product of AB?

Answer 1

0 -5
B= 3 -2
4 0
-6 1

Answer 2

It is a matrix.

Answer 3

\[\large \begin{pmatrix}
-2 & -1 & 5 & 9
\end{pmatrix}\cdot
\begin{pmatrix}
0 & -5\\ 3 & -2\\ 4 & 0\\ -6 & 1
\end{pmatrix}=
\begin{pmatrix}
-37 & 21
\end{pmatrix} \]

Answer 4

Thank you @helder_edwin! Can you please tell me how did you calculate it?

Answer 5

the first matrix if 1by 4 and the second is 4 by 2 so the product is 1 by 2.

you multiply each row of the first matrix with each column of the second matrix. so, for example,
\[\large (\color{red}{-2})\times\color{blue}{0}+(\color{red}{-1})\times\color{blue}{3}+
\color{red}{5}\times\color{blue}{4}+\color{red}{9}\times(\color{blue}{-6})=-37 \]

Answer 6

Matrix multiplication gives me headaches :>

Knowing dot-products makes things sorta simpler to understand...