Question

Write the equation of the parabola with a focus at (-3, -5) and a directrix at y = -7.

Answer 1

The directrix is negative so the equation will be

x^2=4ay

x=-3

y=-5

a=x^2/4y

a=(-3)^2 /4*(-5)

a=9/20

x^2=4*(9/20)*y

x^2=9/5y

Explanation:

The directrix always determine the equation to use. It is also important to notice the sign(-+).