Problem 1
Answers:
- A = 2x2
- B = 2x2
- C = 3x2
- D = 2x3
- E = 3x3
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Explanation:
The size of a matrix is simply the number of rows and the number of columns. Something like 2x3 means we have 2 rows and 3 columns.
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Problem 2
Answers:

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Explanation:
When saying something like
we are looking at the item in the second row and third column of matrix E.
The acronym DNE stands for "Does Not Exist". It's another way of saying "Undefined". For instance, note how matrix E has only 3 columns. When we write
we're asking about something in the fourth column, but no such column exists.
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Problems 3 and 4 seem to be cut off because I don't see them on the screenshot.