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a3 - 9b 3 + (a + b)3
= a3 - b3 + (a+b)3 - 8b3
=a3 - b3 + (a+b)3 - (2b)3
= (a - b)(a2+ab+b2)+(a+b-2b) {(a+b)2 + (a+b). 2b+ (2b)2}
= (a - b) (a2 + ab + b2) + (a – b) (a2 + 2ab + b2 + 2ab +2b2+4b2)
= (a - b) (a2 +ab+b2+a2 + 2ab + b2 + 2ab +2b2+4b2)
= (a-b)(2a2+5ab + 8b2) (ans)
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