To solve this problem you must apply the proccedure shown below:
1. You have that the hyperbola has a vertex at (0,36) and a focus at (0,39).
2. Therefore, the equation of the directrices is:
a=36
a^2=1296
c=39
y=a^2/c
3. When you susbtitute the values of a^2 and c into y=a^2/c, you obtain:
y=a^2/c
y=1296/13
4. When you simplify:
y=432/13
Therefore, the answer is: y = ±432/13
