Parabola intuition 2

Concavity can help to determine what a parabola looks like. See http://jwlchin.blogspot.com/2014/08/recognizing-concavity.html

Substitute a value of x so that the R.H.S of the equation is equal to 0 for the vertical parabola.  

The  distance between the directrix or focus to the vertex =1/(4 * a).  This formula is actually for finding the focus. (focus to vertex)

These hints can help to solve the problem 
https://www.khanacademy.org/math/algebra2/conics_precalc/parabolas_precalc/e/parabola_intuition_2