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A day full of math games & activities. Find one near you.
Which equation represents a parabola that has a focus of (0, 0) and a directrix of y = 2?
x2 = -(y - 1)
x2 = -4y
x2 = -y
x2 = -4(y - 1)
Solution:
Given: Focus of parabola (0, 0) and a directrix of y = 2
Vertex is midway between focus and directrix.
Therefore vertex is at (0, 1)
The vertex form of equation of parabola is y = a(x - h)2 + k
Where vertex h = 0 and k = 1
So the equation of parabola is y = a(x - 0)2 + 1
Distance of vertex from directrix is d = 2 - 1 = 1,
We know d = y = k - 1/4a
2 = 1 -1/4a
1/4a = -1
a = -1/4
Here the directrix is above the vertex, so the parabola opens downward and a is negative.
Therefore, the equation of parabola is y = -1/4x2 + 1
Which equation represents a parabola that has a focus of (0, 0) and a directrix of y = 2?
Summary:
This x2 = -4(y - 1) equation represents a parabola that has a focus of (0, 0) and a directrix of y = 2.
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