Question

Write the general form of the equation which matches the graph below. In complete sentences, explain the process taken to find this equation.

Answer 1

@amistre64 can you help me? :) plz

Answer 2

found it

Answer 3

yay :)

Answer 4

so you need to explain how to find a parabola equation from this

Answer 5

yes

Answer 6

looks like y=4 is a directrex and A is the focus, no?

Answer 7

since a method is involved, and most likely the geometric definition is involved ... my idea wont have much merit

Answer 8

i would use the vertex form: y = a(x-h)^2 + k

input the vertex values for (h,k) and find a by using a latus rectus point ... thats a point on the parabola that is in line with the focus.

Answer 9

so I need to use the vertex form to make the equation?

Answer 10

you need to use what your material wants you to use. i have no material, just a way that a solution can be found.

Answer 11

oh okay, I don't think it shows any specific way I need to use, is that what you would do?

Answer 12

i would use the vertex form, and deduce from the focus (a,b) that a point in the parabola is some (a+c, b) where c is the distance from the vertex to the focus

Answer 13

okay, can you help me do that? ;)

Answer 14

i spose ...

we know the form will take on: y = -a(x-h)^2 + k

right? can you tell me the values of h and k?

Answer 15

is h is 3 and k 0

Answer 16

good,

y = -a(x-3)^2 all we need is a point on the parabola to define the missing variable.

by properties of a parabola, all points are the same distance from the focus as they are from the directrix right?

so we can use a latus rectus point, fancy name for the point that is beside the focus