This is called a difference in two squares.
This expression is equal to

Which means that (a+b) and (a-b) are factors of the first expression.

Here is an example...

Both the x squared and the 16 are perfect squares,
and since the 16 is being subtracted, this is called the difference of two squares.
This means that there are two factors for the expression. They are

You must remember that this process only works when there is
subtraction
occuring between the two squares.

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