\(\text{Ta có : }a+b+c=0\\ \Rightarrow c=-\left(a+b\right)\text{ }\text{ }\text{ }\left(\text{*}\right)\\ \Rightarrow c^3=-\left(a+b\right)^3\\ \Rightarrow a^3+b^3+c^3=a^3+b^3-\left(a+b\right)^3\\ =\left(a^3+b^3\right)-\left(a^3+3a^2b+3ab^2+b^3\right)\\ =-\left(3a^2b+3ab^2\right)\\ =-3ab\left(a+b\right)\text{ }\text{ }\text{ }\text{ }\left(1\right)\\ Thay\text{ }\left(\text{*}\right)\text{ }vào\text{ }\left(1\right),ta\text{ }được:\\ \left(1\right)=\left(-3ab\right)\cdot\left(-c\right)=3abc\left(đpcm\right)\\ \text{ }\text{ }\text{ }\text{ }\text{ }\text{ }\text{ }\)
Vậy \(a^3+b^3+c^3=3abc\)
\(a+b+c=0\Rightarrow a=-\left(b+c\right)\)
\(\Rightarrow a^3+b^3+c^3=[-\left(b+c\right)]^3+b^3+c^3=-3b^2c-3bc^2=-3bc\left(b+c\right)=3abc\)
