Question

When can/can't I add, subtract or multiply matrices together?

Answer 1

have you done matrix multiplication yet?

Answer 2

yes

Answer 3

I think you can't add matries together when they aren't the same size.

Answer 4

http://www.purplemath.com/modules/mtrxadd.htm
This might help.

Answer 5

well... ok.. then you'd know that, matrix multiplication happens LEFT-MATRIX-ROW times RIGHT-MATRIX-COLUMN

so for the multiplication to take place, the RIGHT-MATRIX must have the same amount of COLUMNS as the LEFT-MATRIX amount of ROWS

Answer 6

can you draw an example with random numbers?

Answer 7

@kewlgeek555 i dont really understand what's on the website.. i know how to add them, Im just confused on how many rows and columns there have to be in order to get a solution.

Answer 8

Oh okay.

Answer 9

\(\begin{bmatrix}
a&b&c
\end{bmatrix}\times
\begin{bmatrix}
d&e&f
\end{bmatrix}\qquad \textit{can't multiply, no row/col match}\\ \quad \\

\begin{bmatrix}
a&b&c\\
d&e&f\\
\end{bmatrix}\times
\begin{bmatrix}
g&h&i&\\
j&k&m\\
n&o&p
\end{bmatrix}\qquad \textit{can multiply, notice the matching row/col} \)

Answer 10

but in the 1st one there are even #'s axd axe.. or or?

Answer 11

or no*

Answer 12

yes, the 1st pair have the same dimensions, but for multiplication, that's no feasible
you need to have rows on the left matrix that match the columns on the right matrix

Answer 13

so the rows have to match the columns? and what about addition and subtraction

Answer 14

that's pretty straightforward \(\begin{bmatrix}
a&b\\
c&d
\end{bmatrix}+
\begin{bmatrix}
e&f\\
g&h
\end{bmatrix}\implies
\begin{bmatrix}
a+e&b+f\\
c+g&d+h
\end{bmatrix}\)

Answer 15

okay and is there like a restriction on how many rows and columns there have to be?

Answer 16

no, they just need to be the same dimension

Answer 17

okay:) thank you!

Answer 18

yw