We use cookies to personalise content and advertisements and to analyse access to our website. Furthermore, our partners for online advertising receive pseudonymised information about your use of our website.
Please click on "Accept cookies" if you agree to the setting of cookies. Cookies that do not require consent remain unaffected by this, see
cookie policy and privacy policy.
DECLINE COOKIES

Which equation represents a parabola that has a focus of (0, 0) and a directrix of y = 4?

x^2=−8y

x^2=−8(y−2)

x^2=−2(y−2)

x^2=−2y

jjennylove Feb 6, 2019

#1**+2 **

If the directri is y = 4 and the focus is (0,0).....the vertex = (0, (0 + 4)/2 ) = (0, 2 )= (h, k)

In other words....the vertex is midway between the focus and the directrix

p is the distance between the vertex and the focus = 2

And since the directrix is above the focus, the parabola opens downward

And we have the form

-4p ( y - k) = x^2

-4p(y-2) = x^2 (we use the " - " because the parabola opens downward )

- 4(2) (y -2) = x^2

-8(y - 2) = x^2

EDIT TO CORRECT AN ERROR

CPhill Feb 6, 2019