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Find equation of directrix of parabola, x2 = - 22y .
1. 2y - 11 = 0 
2. 2x - 11 = 0
3. 2x + 11 = 0 
4. 2y + 11 = 0

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Correct Answer - Option 1 : 2y - 11 = 0 

Concept: 

Parabola,  x2 = 4ay, where a > 0, then  

Equation of directix,  y + a = 0

Parabola, x2 = - 4ay, where a > 0, then 

Equation of directix, y - a = 0 

Calculation: 

Given parabolic equation,  x2 = - 22y 

On comparing with standard equation, x= -4ay , we get a \(\frac{11}{2}\) 

We know that equation of directrix, y - a = 0

⇒ y - \(\frac{11}{2}\) = 0

⇒ 2y - 11 = 0 . 

The correct option is 1. 

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