Question

Derive the equation of the parabola with a focus at (−5, 5) and a directrix of y = -1.

f(x) = −one twelfth (x − 5)2 + 2

f(x) = one twelfth (x − 5)2 + 2

f(x) = −one twelfth (x + 5)2 + 2

f(x) = one twelfth (x + 5)2 + 2

Can you please help me out? I'm stuck on this @paki

Answer 1

@Callisto can u pleaase please help me?!

Answer 2

@thomaster Can u plz help?

Answer 3

@dan815

Answer 4

@robtobey PLEASE HELP!!

Answer 5

@jim_thompson5910 PLEASE HELP ME!! :( Ur the only person I have faith in xD

Answer 6

compare the y coordinates of the focus and the directrix

which one is larger?

Answer 7

y coordinate of the focus is larger @jim_thompson5910

Answer 8

so this means the parabola opens upward

Answer 9

which equations can we eliminate?

Answer 10

A and B @jim_thompson5910

Answer 11

no

Answer 12

which parabolas open downward?

Answer 13

idk @jim_thompson5910

Answer 14

look for the leading coefficient when it is negative

Answer 15

oh ok so the parabolas that open downward would be A and C? @jim_thompson5910

Answer 16

correct, we can eliminate A and C

Answer 17

yes @jim_thompson5910

Answer 18

now notice the focus has an x coordinate of -5

Answer 19

therefore h = -5

Answer 20

plug that into a(x-h)^2 + k and what do you get?

Answer 21

dont know how to do that sorry :/

Answer 22

replace h with -5 and simplify

Answer 23

tell me what you get

Answer 24

ok so a(x-(-5)^2 +5?

Answer 25

@jim_thompson5910

Answer 26

then the x-(-5) simplifies to what?

Answer 27

x+5

Answer 28

so that is why the answer is D

B has x-5 when it should be x+5

Answer 29

So its D

Answer 30

yaaaaayyy!! thank youu!! :)

Answer 31

np