(A) Let $\Delta=\left|\begin{array}{lll}1 & 1 & 1 \\ a & b & c \\ a^{3} & b^{3} & c^{3}\end{array}\right|$.
Applying $C_{1} \rightarrow C_{1}-C_{2}$ and $C_{2} \rightarrow C_{2}-C_{3}$,we have:
$\Delta=\left|\begin{array}{ccc}0 & 0 & 1 \\ a-b & b-c & c \\ a^{3}-b^{3} & b^{3}-c^{3} & c^{3}\end{array}\right|$.
Taking common factors $(a-b)$ from $C_{1}$ and $(b-c)$ from $C_{2}$:
$\Delta=(a-b)(b-c)\left|\begin{array}{ccc}0 & 0 & 1 \\ 1 & 1 & c \\ a^{2}+ab+b^{2} & b^{2}+bc+c^{2} & c^{3}\end{array}\right|$.
Applying $C_{1} \rightarrow C_{1}-C_{2}$:
$\Delta=(a-b)(b-c)\left|\begin{array}{ccc}0 & 0 & 1 \\ 0 & 1 & c \\ a^{2}-c^{2}+ab-bc & b^{2}+bc+c^{2} & c^{3}\end{array}\right|$.
$\Delta=(a-b)(b-c)\left|\begin{array}{ccc}0 & 0 & 1 \\ 0 & 1 & c \\ (a-c)(a+c)+b(a-c) & b^{2}+bc+c^{2} & c^{3}\end{array}\right|$.
$\Delta=(a-b)(b-c)(a-c)\left|\begin{array}{ccc}0 & 0 & 1 \\ 0 & 1 & c \\ a+b+c & b^{2}+bc+c^{2} & c^{3}\end{array}\right|$.
Expanding along $R_{1}$:
$\Delta=(a-b)(b-c)(a-c)(1)[0 - (a+b+c)] = -(a-b)(b-c)(a-c)(a+b+c)$.
Since $-(a-c) = (c-a)$,we get:
$\Delta=(a-b)(b-c)(c-a)(a+b+c)$.
Hence,the result is proved.