（a+b+c）(a^2+b^2+c^2-ab-bc-ca)＝a^2(a+b+c)+b^2(a+b+c)+c^2(a+b+c)-ab(a+b+c)-bc(a+b+c)-ca(a+b+c) =a^3+a^2b+a^2c+b^2a+b^3+b^2c+c^2a+c^2b+c^3-a^2b-ab^2-abc-abc-b^2c-bc^2-a^2c-abc-c^2a =a^3+b^3+c^3-3abc...