You can
put this solution on YOUR website! IS the following binomial a difference of squares?
9a² - 8b²
No because 8 is not a perfect square.
Edwin
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PS:
Note that if the 8 had been, say a 4, and it had been
9a² - 4b²
instead, then it could have been written as
(3a)² - (2b)²
and then it would have been a difference of squares.
But with the 8 it is not.