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Mathematics

Matrix Multiplication and the Rules That Govern It

Quick fact

In matrix multiplication, the number of columns in the first matrix must exactly equal the number of rows in the second. If they don't match, the multiplication is undefined—no alternatives.

Why this is interesting

You might think multiplying matrices is just like multiplying numbers, but that's a trap. What if I told you that swapping the order of multiplication can give you a completely different result, or even be impossible?