Mathematics

Problem

Let the line

lx + my = 1

intersects the parabola

y^2 = 4ax

at points

P

and

Q

. The normals at

P

and

Q

meet at point

R

. If

R

lies on the parabola

y^2 = 4ax

, the

a

equals

\frac{1}{l}

\frac{1}{2l}

-\frac{1}{l}

-\frac{1}{2l}