Matrices help

[9_7]

Hey guys I was wondering if you had a 4x5 matrix, and you couldn't multiply it with a 4x2 matrix, could you switch the 4x5 matrix into a 5x4 matrix in order to make the multiplication work? Thanks

[Yendall]

Hey guys I was wondering if you had a 4x5 matrix, and you couldn't multiply it with a 4x2 matrix, could you switch the 4x5 matrix into a 5x4 matrix in order to make the multiplication work? Thanks

Depends what the question is asking. If the question is asking for the product of AB where A = 4x5 and B = 4x2, then the answer would be: Non-Defined.

Which question are you attempting?

[MagicGecko]

NO!, you can't just switch around the number of rows and columns to you liking.
and anyway Yendall is right the question will be Non-defined.

[Yendall]

NO!, you can't just switch around the number of rows and columns to you liking.
and anyway Yendall is right the question will be Non-defined.

Also, if you're listing, say, prices of items. There are two items and you want to find the total spendings on the items when 'x' people buy a certain quantity. Prices of two items are:
$2
$3
John is buying 4 of item 1
John in buying 5 of item 2
Find the total price
You need to find the total price, being a singular amount:


If you swap the column and row matrices, you will end up with a different order and thus a different answer/matrix. This will be zero marks on the exam if you do not produce the correct order.


I know that this isn't really 'swapping' rows and columns, but it is also vital that you pay close attention to the question. You must have the correct order or you will produce an incorrect answer. You must remember that swapping matrices can also lead to incorrect answers.