9. Perfect Squares
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Rewrite the given expression so that it is easier to make groups.
2a(b+1)(b-1)(a-b)
To factor by grouping, we will take the greatest common factor of the first pair of terms and the greatest common factor of the second pair of terms.
Factor out 2a^2
Factor out -2ab
Notice that (b^2-1) and 2a are factors of both terms, so we can factor them out.
Factor out ( b^2-1 )
Factor out 2a
a^2-b^2=(a+b)(a-b)