Find the equation of the directrix of the parabola x2 = 6y ?

  1. y = 3/2
  2. y = - 2/3
  3. y = - 3/2
  4. y = 2/3

Answer (Detailed Solution Below)

Option 3 : y = - 3/2
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Detailed Solution

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CONCEPT:

The following are the properties of a parabola of the form: x2 = 4ay where a > 0

  • Focus is given by (0, a)
  • Vertex is given by (0, 0)
  • Equation of directrix is given by: y = - a
  • Equation of axis is given by: x = 0
  • Length of latus rectum is given by: 4a
  • Equation of latus rectum is given by: y = a

CALCULATION:

Given: Equation of parabola is x2 = 6y

The given equation of parabola can be re-written as: x2 = 4 ⋅ (3/2)y----------(1)

Now by comparing the equation (1) with x2 = 4ay we get

⇒ a = 3/2

As we know that, the equation of directrix of the parabola of the form x2 = 4ay is given by: y = - a

So, the equation of directrix of the given parabola is: y = - 3/2

Hence, option C is the correct answer.

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