Question

factorise this question​

Answer 1

a³ - 27b³ -7a²b -21ab²

= [a³ - (3b)³] -7ab(a-3b)

= (a-3b)[a²+a(3b)+(3b)²]-7ab(a-3b)

=(a-3b)[a²+3ab+9b²-7ab]

=(a-3b)(a²-4ab+9b²)

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