Question

Parabola help

Answer 1

I 4got how to get the equation of a parabola when given 3 points. I have (0,0) & (5.5,9) & (-5.5,9) how do I get this into ax^2+ bx + c which is the parabolic equation I believe

Answer 2

maybe we just substitute and solve - 3 equations 3 unknowns ?

Answer 3

ax^2+bx+c goes thru (0,0)

a(0)^2+b(0)+c = 0
c = 0 ------------------(1)

Answer 4

so c-0? that means then the foci would be (0, 1/4) right?

Answer 5

@ganeshie8

Answer 6

hmm im not sure if we can figure out focus yet, how did u get that ? :)

Answer 7

Oh whoops used a different thing ok so on my lesson it says foci can be found by doing (h, k+c)
Oh and if this helps vertex is 0,0

Answer 8

ohk :) vertex is (0, 0 ) yes.. cuz 5.5 & -5.5 give same value 9. and they are at same distance from y axis

Answer 9

that gives h = 0, k = 0

Answer 10

And c is 0?

Answer 11

we got that, focus = (h, k+1/4a)

Answer 12

K so (0,1/4a) how do we solve for a?

Answer 13

c = 0 is first equation,

since it goes thru (5.5,9),

a(5.5)^2+b(5.5)+0 = 9 -------------(2)

since it gors thru (-5.5, 9),

a(-5.5)^2+b(-5.5)+0 = 9 -------------(3)

Answer 14

solving (1), (2), (3) gives,
a = 0.2975
b = 0
c = 0

so, the required parabola is y = 0.2975x^2

Answer 15

Well a=1/4c and hey why do u put a bunch of dashes then a number in parenthesis next to it?

Answer 16

ha that works :)

Answer 17

just to label it as equation (2), equation (3) etc...

Answer 18

Oh ok :)

Answer 19

so focus wud be (h, k+1/4a) = (0, 0+1/4(0.2975))

Answer 20

Wow nice yeah parabola intersects the points and k foci is (0,.84) approximate

Answer 21

yup (0, .84) is focus, so that gives directrix as y = -.84
it all boild down to solving system of equations i think

Answer 22

ok i see :p yeah I'm doing a conic section solar cookerr project thing & 4got how 2 find equation and foci of parabola, thx a ton :)

Answer 23

wow parabolic mirrors... hows it going ?

Answer 24

Need to poke something through the foci now and once I'm done with it I have to cook something with it :p

Answer 25

ive tried it using my dish antenna once.. it was a fail lol... couldnt complete it :(

Answer 26

oh is that for fun.. or wat ? :)

Answer 27

Lol that sucks :D after this then I can take my finals for algebra II

Answer 28

ohk... nice :) good luck wid the project :))

Answer 29

Thx :)