A ray of light is coming along the line `y=b` from the positive direction of x-axis and striks a concave mirror whose intersection with xy-plane is a parabola `y^2 = 4ax`. Find the equation of the reflected ray and show that it passes through the focus of the parabola. Both `a and b` are positive.

Answer

(y−b)(4a
2
−b
2
)=−b(4ax−b
2
)