-(a+1)²+9(a-2)²
=[3(a-2)+(a+1)][3(a-2)-(a+1)]
=(4a-5)(2a-7)
(7a²+2b²)²-(2a²+7b²)²
=[(7a²+2b²)+(2a²+7b²)][(7a²+2b²)-(2a²+7b²)]
=(9a²+9b²)(5a²-5b²)
=45(a²+b²)(a+b)(a-b)
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