If $a + b + c = 0$, then $a^{3}+b^{3}+c^{3}$ equals

If $a + b + c = 0$, then $a^{3}+b^{3}+c^{3}$ equals
  1. $3abc$
  2. $0$
  3. $abc$
  4. $-3abc$

Solution

Identity: $a^{3}+b^{3}+c^{3} - 3abc = (a+b+c)(a^{2}+b^{2}+c^{2}-ab-bc-ca)$. If $a+b+c=0$, the right side is $0$, so $a^{3}+b^{3}+c^{3}=3abc$.

Asked in: IMO

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