Question

how do I find the foci of a parabola

Answer 1

http://hotmath.com/hotmath_help/topics/focus-of-a-parabola.html

Answer 2

how do I find 1/4a

Answer 3

the focus can be found from the vertex form of the parabola

y = a(x - h) + k

Answer 4

note this is for a parabola with a vertical axis of symmetry

Answer 5

is it true that 1/4c=1

Answer 6

it depends what you mean by c

Answer 7

I do know like the basic formula but I keep on getting a messed up answer according to the calculator

Answer 8

how do I find the c

Answer 9

what formula are you talking about?

Answer 10

On the book, it mentions (h,k+c)

Answer 11

if the vertex is not on (0,0)

Answer 12

The equation I got was y=-3x^2+3

Answer 13

tell me which formula you mean

Answer 14

y=1/4c(x-h)^2+k

Answer 15

Is a -3?

Answer 16

Oh I'm sorry I got that wrong
Its 1/4a not (1/4) a

Answer 17

thats ok

Answer 18

lets find the focus of y = -3x^2 + 3 step by step

Answer 19

yes

Answer 20

that would be helpful

Answer 21

first we convert the equation to vertex form

there is no term in x so the equation becomes ( h = 0):-

y = ax^2 + k

so a = -3 , h = 0 and k = 3

focus = ( h k+ 1/4a) = (0, 3 + 1/4(-3))
= (0, 3 - 1/12)
= (0, 35/12)

Answer 22

any questions?

Answer 23

how is the equation y=ax^2+k

Answer 24

well because h = 0

y = a(x-h)^2 + k

our equation is -3 x^2 + 3

comparing this with the above standard form
a = -3 and k = 3 but theres is no -h so h = 0

Answer 25

if you like we can write out equation as

y = -3 (x - 0)^2 + 3
comparing with
y = a(x - h)^2 + k

we see that h = 0.

Answer 26

Ohhh now I'm getting it

Answer 27

good

Answer 28

and c= 1/4a?

Answer 29

if you write the y coordinate of the focus as k +c then c = 1/4a Yes.

Answer 30

ok I think I'm good but I gotta make sure

Answer 31

I got up to y=-3x^2+3

Answer 32

so do I input K+1/4a into y?

Answer 33

yes