What is the equation of the directrix of the parabola y2−8y−4x+4=0y^2 - 8y - 4x + 4 = 0y2−8y−4x+4=0?
x=0x = 0x=0
x=−1x = -1x=−1
x=1x = 1x=1
x=2x = 2x=2