- #1

- 1,752

- 1

3D + E

D = 2 x 3

-1 2 3

4 0 5

E = 3 x 2

2 1

8 -1

6 5

D has 3 columns, and E has 3 rows ???

D = 2 x 3

-1 2 3

4 0 5

E = 3 x 2

2 1

8 -1

6 5

D has 3 columns, and E has 3 rows ???

Last edited:

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- Thread starter rocomath
- Start date

- #1

- 1,752

- 1

3D + E

D = 2 x 3

-1 2 3

4 0 5

E = 3 x 2

2 1

8 -1

6 5

D has 3 columns, and E has 3 rows ???

D = 2 x 3

-1 2 3

4 0 5

E = 3 x 2

2 1

8 -1

6 5

D has 3 columns, and E has 3 rows ???

Last edited:

- #2

- 1,752

- 1

Oh crap, ignore me ... LOL, I'm thinking inner product rules ... :p

- #3

HallsofIvy

Science Advisor

Homework Helper

- 41,833

- 963

The product DE is also defined but ED is not. Is that what you are talking about? Do I get a prize for guessing that?

The product of of two matrices, A and B can be defined as "the ij-component is the dot product of vectors consisting of the ith row of A and the jth column of B".

ED is not defined because each row of E has 2 components while each column of D has 3 components. You cannot take the dot product of two such vectors.

As you point out, the number of columns of D and the number of rows of E are the same- that is why DE

- #4

- 1,752

- 1

- #5

cristo

Staff Emeritus

Science Advisor

- 8,107

- 73

Perhaps less skimming and more 'doing' is in order!I'm not actually doing the problem, just skimming through the section.

- #6

- 1,752

- 1

LOL, I know I should be doing the problems :( But, I did the examples and looked over the rules. I plan on doing a a good review after finals :)Perhaps less skimming and more 'doing' is in order!

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