A parabola mirror is kept along `y^2=4x` and two light rays parallel to its axis are reflected along one straight line. If one of the incident light rays is at 3 units distance from the axis, then find the distance of the other incident ray from the axis.

Explanation

We have parabola `y^(2)=4x`.
Let two incident rays AP and BQ, which are parallel to axis of the parabola, strikes the parabola at points A and B, respectively.
After reflection, both the pass through the focus S(1,0).

Therefore, AB is focal chord.
Let point A be `(t^(2),2t)`.
Distance of ray AP is 3 units from axis.
`:." "2t=3`
`or" "t=(3)/(2)`
Coordinates of point B are `((1)/(t^(2)),(-2)/(t))` (other end of focal chord).
Distance of B from the axis `=(2)/(t)=(4)/(3)`