The straight line joining any point P on the parabola y²=4ax to the vertex and perpendicular from the focus to the tangent at P, intersect at R, then the equation of the locus of R is
a. 2x²+y²-2ax=0
b. x²+2y²-ax=0
c. 2x²+2y²-ay=0
d. 2x²+y²-2ay=0