Problem

Let

A

and

B

be two distinct points on the parabola

y^2 = 4x

. If the axis of the parabola touches a circle of radius

r

having

AB

as its diameter, The slope of the line joining

A

and

B

can be a.

-\frac{1}{r}

\frac{1}{r}

\frac{2}{r}

-\frac{2}{r}