1.

The directrix of the parabola `x^2-4x-8y + 12=0` isA. y=0B. x=1C. y= -1D. x = -1

Answer» Correct Answer - C
We have, `x^(2)-4x-8y+12=0rArr(x-2)^(2)=8(y-1)" …(i)"`
Clearly, it represents a parabola with vertex at (2, 1) and latusrectum = 8. Shifting the origin at (2, 1), we have `x=X+2" and "y=Y+1" ….(ii)"`
Substituting these in (i), we get
`X^(2)=8Y`
It represents a parabola whose directrix has the equation
`Y=-2" "[because" y=-a is the directrix "x^(2)="4ny"]`
`"or, "y=-1" "["Using (ii)"]`


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