Correct Answer - Option 1 : 4x2
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
Here, we have to find the equation of the parabola with vertex at origin, passing through the point (3, -4) and symmetric about the y-axis.
It is given that the vertex of the parabola is at (0, 0) and it is symmetric about the y-axis.
So, the equation of parabola can be either x2 = 4ay or x2 = -4ay
But since the parabola passes through the point P (3, - 4) and the point P lies in the 4th quadrant
i.e the parabola is facing downwards
So, the equation of the parabola is of the form x2 = -4ay
∵ The point P (3, -4) passes through the parabola so, x = 3 and y = -4 will satisfy the equation x2 = -4ay
⇒ 32 = - 4 ⋅ a ⋅ (-4)
⇒ a = 9/16
So, the required equation of parabola is: x2 = -4 ⋅ (9/16)y
⇒ 4x2 = -9y
Hence, option A is the correct answer.