Hi guys, need help with this proof, have spent a while on it and getting no where.

I followed the hint but couldn't do anything useful

Suppose that the cubic polynomial x^3 + Ax + B factors into (x-a)(x-b)(x-c)

Prove that 4A^3 + 27B^2 = 0 if and only if two (or more) of a, b, c are the same. (Hint. Multiply out the right-hand side and compare coefficients to relate A and B to a,b,c)

Cheers for the help!