Find the area of triangle inscribed in the parabola $y^2=4ax$ with vertices $(x_1,y_1),(x_2,y_2)$ & $(x_3,y_3)$?

Question

$\begin{array}{1 1}(a)\;\large\frac{1}{8a}\normalsize \mid(y_1-y_2)(y_2-y_3)(y_3-y_1)\mid\\(b)\;\large\frac{1}{8a}\normalsize \mid(y_1+y_2)(y_2+y_3)\mid\\(c)\;\large\frac{1}{8a}\normalsize \mid(y_1-y_2)(y_2-y_3)\mid\\(d)\;\large\frac{1}{2a}\normalsize \mid(y_1-y_2)(y_2-y_3)\mid\end{array}$