Question 984603
Knowing vertex and focus, you can find the directrix.;  the distance between vertex and the focus is the same distance between the vertex and the nearest point on the directrix.


The number p is the distance between the vertex and the focus.  Knowing p and the vertex, you can write an equation for the parabola directly.  


Your parabola opens toward the left, so you will have a form like  {{{4p(y-h)=-(x-h)^2}}}.


Either or both of these video presentations will help:

<a href="https://www.youtube.com/watch?v=M8LGsQMwwj4">Equation of parabola, vertex at origin - Derivation</a>
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<a href="https://www.youtube.com/watch?v=Wworlx39KfQ">Equation of parabola, vertex not at origin, focus and directrix given - general</a>