I will explain how to multiply matrices. (If that's not what you meant by the multiplication law, I apologize for misunderstanding.)
There is some information on Multiplication of Matrices here on Socratic.
I think of it as a process that is easier to explain in person, but I'll do my best here.
Let's go through an example:
Find the first row of the product
Take the first row of
It looks like:
Now multiply times the first column and add to get the first number in the first row of the answer:
The product starts with:
Next multiply times the second column and add to get the second number in the first row of the answer:
The first row of the product is:
A this point we know that the product looks like:
Find the second row of the product
Find the second row of the product by the same process using the second row of
The second row of the product is:
Write the answer