Equation for an ellipse with center (0,0), vertices (3,0) and (-3,0), and foci (2,0) and (-2,0)?

Question

anonymous · Answer

a. x^2/9+y^2/4=1
b. x^2/5+y^2/9=1
c. x^2/9+y^2/5=1
d. x^2/4+y^2/9=1

nottim · Answer

dunno what a foci is

nottim · Answer

really, i dunno what this is in general

nottim · Answer

may i offer the services of wolfram alpha to help?

anonymous · Answer

At this point PLEASE!

anonymous · Answer

Can you provide me with a link

amistre64 · Answer

|dw:1333407979574:dw|

amistre64 · Answer

center to vertex = 3

center to focus = 2

a^2 = 3^2 + 2^2 = 13

a = sqrt(13); so we should have a 9 and a 13 in the denoms

amistre64 · Answer

hmmm

amistre64 · Answer

the denoms measure the 1/2 axis after we sqrt them

amistre64 · Answer

sqrt(9) = 3

sqrt(n) = sqrt(13); n = 13

what am i missing?

anonymous · Answer

Hmm... I'm just confused. But I understand your useful explanation

amistre64 · Answer

|dw:1333408216198:dw|

i had my verts in the wrong spots :)

amistre64 · Answer

9-4 = 5

sqrt(5)^2 = 5

x/9 and y/5 should do it

anonymous · Answer

Oh o.k. Now it makes sense. Thanks amistre64. You're the best

amistre64 · Answer

good luck