Rút gọn : (a+b+c)^3 +(a-b-c)^3

$\begin{array}{l}
{\left( {a + b + c} \right)^3} - {\left( {a - b - c} \right)^3}\\
 = {\left[ {a + \left( {b + c} \right)} \right]^3} + {\left[ {a - \left( {b + c} \right)} \right]^3}\\
 = {a^3} + {\left( {b + c} \right)^3} + 3a\left( {b + c} \right)\left( {a + b + c} \right) + \left[ {{a^3} - 3a\left( {b + c} \right)\left( {a - b - c} \right) - {{\left( {b + c} \right)}^3}} \right]\\
 = 2{a^3} + 6a{\left( {b + c} \right)^2}\\
 = 2{a^3} + 6a\left( {{b^2} + 2bc + {c^2}} \right)\\
 = 2{a^3} + 6a{b^2} + 12abc + 6a{c^2}
\end{array}$