(x-a)³+(x-b)³+(x-c)³-3(x-a)(x-b)(x-c)
we know that
a^3 + b^3 + c^3 =3abc
or, a+b+c = 0
so, x - a + x -b +x - c = 0
or, 3x - ( a + b + c) = 0
or, 3x - 0 = 0
or, x = 0
we put the value of x in it
we get , (-a)^3 +(-b)^3 +(-c) ^3 +3abc
we know that 3abc = a^3 + b^3 + c^3
=> - a^3 - b^3 -c^3 + a^3 + b^3 + c^3
= 0