The directrix of the parabola `x^2-4x-8y + 12=0` is

Explanation

Given

`x^{2}-4 x-8 y+12=0 `

`Rightarrow(x-2)^{2}-4-8 y+12=0 `

`Rightarrow(x-2)^{2}=8 y-8 `

`Rightarrow(x-2)^{2}=8(y-1) `

Putting ` X=x-2, Y=y-1`

`X^{2}=8 Y` Comparing with ` X^{2}=4 a Y a=2 `

Equation of the directrix `Y=-a `

...