Factorise :
a2 - 81(b - c)2
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Given,
= (a)2 - [9(b - c)]2
= [a + 9(b - c)][a - 9(b - c)]
= (a + 9b - 9c)(a - 9b + 9c).
Hence, a2 - 81(b - c)2 = (a + 9b - 9c)(a - 9b + 9c).
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