# Thread: Parabolas: Given the Directrix and Vertex. Find "P"

1. ## Parabolas: Given the Directrix and Vertex. Find "P"

Vertex: (1,1)

Directrix: Y = 9/8

2. Originally Posted by AirSaints
Vertex: (1,1)

Directrix: Y = 9/8

recall that "P" is a collection of points on the parabola such that

$
d(F,P)=d(P.D)

$

so in this case since we only know where the Vertex is and Diretrix
we can only give the value of one point of P which is the vertex itself

the distance from the vertex to the directrix is 1/8 and the distance from the vertex to the focus is 1/8

3. recall that "P" is a collection of points on the parabola such that
d(FP)= d(DP)
Uh, bigwave, using that definition, "P" is the parabola itself. The wikipedia article Wilmer links to uses "P" mean the distance from the vertex to the focus which, as Wilmer points out, is the same as the distance from the vertex to the diretrix, 1/8. P= 1/8.