Question

What is the equation of the directrix for the conic section shown below?
x^2=24y
A. y = 9
B. x = 4
C. x = -9
D. y = -6

Answer 1

@campbell_st

Answer 2

@campbell_st

Answer 3

well a standard form of the parabola with the vertex at the origin is

\[x^2 = 4ay\]

so looking at your question, the parabola is concave up...

the vertex is at the origin...

a is called the focal length...

what value does a have... when you compare your equation to the standard form I posted..?

Answer 4

20?

Answer 5

well you need to compare

4a = 24

what is the value of a...?

Answer 6

a=6

Answer 7

@campbell_st

Answer 8

great.. so the focal length is correct...

the directrix is a units below the vertex...



so what do you think the equation of the directrix is..?