Find the point of intersection of tangents at any two points on the parabola $y^2=4ax$?

Question

$\begin{array}{1 1}(a)\;x=at_1t_2\\(b)\;x=2at_1t_2\\(c)\;x=a(t_1+t_2)\\(d)\;x^2=a(t_1t_2)\end{array}$