Using a directrix of y = 5 and a focus of (4, 1), what quadratic function is created?

f(x) = 1/4 (x - 4)^2 - 3

f(x) = 1/8 (x + 4)^2 - 3

f(x) = -1/8 (x - 4)^2 + 3

f(x) = -1/4 (x + 4)^2 - 3

Question

Using a directrix of y = 5 and a focus of (4, 1), what quadratic function is created?

 f(x) = 1/4 (x - 4)^2 - 3

 f(x) = 1/8 (x + 4)^2 - 3

 f(x) = -1/8 (x - 4)^2 + 3

 f(x) = -1/4 (x + 4)^2 - 3

anonymous · Answer

@KirbyLegs and @mathstudent55 could you help with this one?

anonymous · Answer

It is either A or C

This is because of the parenthesis (x+4) and (x-4)
The x value is 4, meaning that it will have to have (x-4)
x-4 = 0
x = 4

It's either A or C

anonymous · Answer

Thank you @KirbyLegs

anonymous · Answer

Now you can look at the slopes.
One has 1/4, the other has -1/8

The slope you are looking for is positive

Meaning that the answer is A

Does that make sense?
I kind of use the choices to my advantage but multiple choice questions let you do that.

anonymous · Answer

Yes i do understand now. Thank you so much!