Posted by **victor** on Wednesday, August 3, 2011 at 8:25am.

Find the equation of the parabola with the vertex at the origin and directrix y =5

- mathematics -
**Henry**, Wednesday, August 3, 2011 at 9:34pm
The vertex is mid-way between the directrix and focal point:

D(0,5)

V(0,0)

F(0,y)

FV = VD = 1/4a = 5,

0 - y = 5,

Y = -5.

1/4a = 5,

Multiply both sides by 4a:

20a = 1,

a = 1/20.

Vertex Form: Y = a(x-h)^2 + k,

Y = 1/20(x-0)^2 + 0,

Eq: Y =(1/20)x^2

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