If the focal chord of the parabola y2=ax is 2x−y−8=0, then the equation of directrix is.
x + 4 = 0
Focal chord is any chord of a parabola which passes through the focus of the parabola. Here the given parabola is,
y2=4ax
focus = (a, 0)
focal chord is given as,
2x - y - 8 = 0.This passes through (a, 0)
2a - 0 - 8 = 0
a = 4
∴ equation of directrix is,
x + 4 = 0