9514 1404 393
Answer:
C. 1/(4a)
Explanation:
We assume you're comparing the vertex form ...
y = a(x -h)^2 +k
to the form used to write the equation in terms of the focal distance p.
y = 1/(4p)(x -h)^2 +k
That comparison tells you ...
a = 1/(4p)
p = 1/(4a) . . . . . . multiply by p/a; matches choice C
__
Additional comment
When using plain text to write a rational expression, parentheses are needed around any denominator that has is more than a single constant or variable. The order of operations requires 1/4a to be interpreted as (1/4)a. The value of p is 1/(4a).
When rational expressions are typeset, the fraction bar serves as a grouping symbol identifying the entire denominator:
