Question

if a = 3+b, prove that a cube - b cube - 9ab = 27​

Answer 1

It is given, a + b = 3

∴ a³ + b³ + 9ab

= a³ + b³ + 3ab × 3

= a³ + b³ + 3ab (a + b)

= (a + b)³ = (3)³ = 27.

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