What is the product of the two binomials (3a+4b)(3a-4b)

To find the product of two binomials, I like to use a method called FOIL. F: first, O: outer, I: inner, L: last. 
So, first I am going to multiply the first numbers of the binomials, 3a and 3a to get 9a²
Second, I am going to multiply the outer numbers of the binomials, 3a and -4b to get -12ab
Third, I am going to multiply the inner numbers of the binomials, 4b and 3a to get 12ab
Fourth, I am going to multiply the last numbers of the binomials, 4b and -4b to get -16b²
Fifth, I am going to add all of the products together.
9a²-12ab+12ab-16b²
The expression that is left is 9a²-16b²
I hope I did this right!

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