$(a - b)^{3}$ expands to

$(a - b)^{3}$ expands to
  1. $a^{3} - 3a^{2}b + 3ab^{2} - b^{3}$
  2. $a^{3} - b^{3}$
  3. $a^{3} - 3ab^{2} + b^{3}$
  4. $(a-b)(a^{2}+ab+b^{2})$

Solution

Standard binomial cube identity for difference.

Asked in: IMO

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