Defined or Undefined

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frctl

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Jun 29, 2019
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E is (5 x 4)
B is (4x 5)
A is (4 x 5)

I have to solve the following:
E(5B + A)
(5 x 4)(5((4 x 5) + (4 x 5))

Is this defined or undefined?
 
frctl said:
E is (5 x 4)
B is (4x 5)
A is (4 x 5)

I have to solve the following:
E(5B + A)
(5 x 4)(5((4 x 5) + (4 x 5))

Is this defined or undefined?
Click to expand...
Are 'E', 'B' & 'A' matrices or numbers like 20?
 
What have you thought about the question? Can you multiply B by 5? Can you add 5B and A? Can you multiply that on the left by E?
 
The standard notation, n x m matrix, means that the matrix has n rows and m columns. In order to be able to add or subtract two matrices, they must have the same dimensions, they must both be n x m matrices. in order to multiply two matrices, AB, the number of columns of A must be the same as the number of rows of B: (p x m) times (m x q) giving a p x q matrix.

Here, A and B are 4 x 5 matrices so 5A+ B is a 4 x 5 matrix. E is a 5 x 4 matrix so E(5A+ B) is 5 x 4 times 4 x 5. Yes, that can be done.

(It would have been a good idea to tell us initially that A and B were 4 x 5 matrices. My first thought was "okay, A= B= 4 x 5= 20"!)
 
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