Question

Ellipses

Answer 1

@freckles

Answer 2

@rational

Answer 3

oh I know where I calculated wrong.
in that
c/a and forgot that a was =4 and not 2

Answer 4

would it be
b^2 = 2?

Answer 5

nope that's not right either.

Answer 6

@rvc do you know how to do these?

Answer 7

@jim_thompson5910

Answer 8

bad at circle and conics
sorry :(

Answer 9

Thanks for looking at it though. Ah well.

Answer 10

@divu.mkr help please :)

Answer 11

first off we find a from the major axis
a= 4
then we find c by looking at the eccentricity
c/a = sq7/2

Answer 12

focii on y axis means that the major axis is on Y aix and you are given with the length of major axis and ecc.. you can find minor axis from that data

Answer 13

axis**

Answer 14

It would have a vertical major axis so (x-h)^2/b^2 + (y-k)^2/a^2 =1

where 2b=8

Answer 15

how do I find the minor axis in there?

Answer 16

eccentricity = sqrt(a^2-b^2)/a

Answer 17

b^2 = a^2(1-e^2)

Answer 18

so from this you can find the minor axis

Answer 19

hmm

Answer 20

focii are on the y-axis so h=0

Answer 21

so
x^2/8 + y^2/16 = 1

Answer 22

is that the answer?

Answer 23

@iambatman save me. lol

Answer 24

Hollllllaaaa

Answer 25

aloo

Answer 26

major axis = 8 ye?

Answer 27

I just need to find an equation :P

Answer 28

yeah

Answer 29

major axis = 2a
so a = 4

Answer 30

Yes good :P
\[e = \frac{ c }{ a } ~~~\text{and}~~~ c^2 = a^2-b^2\]

yes yes this looks good, it will work out nicely

Answer 31

Ok so notice we're given the eccentricity (e) and it tells us the Foci is on the y - axis, this is important because the foci are ALWAYS on the major axis. So will the major axis run vertically or horizontally?

Answer 32

vertically?

Answer 33

That sounds good, so what should we do next

Answer 34

You should already realize an error in your work with that information

Answer 35

a should be the bigger one?

Answer 36

You're too good :)

Answer 37

Aw, shucks.

Answer 38

so what numbers do i flip around?

Answer 39

Well lets find b first

Answer 40

To do that we have \[e = \frac{ c }{ a }\] and \[c^2 = a^2 - b^2\]

Answer 41

e = sq7/2
but we're given that a = 4 so do we double that whole thing?

Answer 42

What was that cute game we were playing earlier? I had a name for it

Answer 43

lol substitution?

Answer 44

Yeah that's it ;)

Answer 45

but we're given the e!

Answer 46

So what's stopping you from solving for c :)

Answer 47

no b?

Answer 48

We have a and e!

Answer 49

ooh oh

Answer 50

sq7/2=c/4

Answer 51

:))))

Answer 52

So what will be our c value?

Answer 53

sq14?

Answer 54

\[2\sqrt{7}\]

Answer 55

Looks good, now what's our next step :)

Answer 56

find b!

Answer 57

Right, and how will we do that

Answer 58

so that's just c, not c^2

Answer 59

Yes good observation!

Answer 60

so now
c^2=a^2+b^2

Answer 61

Stop right there for a second!

Answer 62

o.o yes sir.

Answer 63

Lets look at the equation you said, what is that for :)

Answer 64

c

Answer 65

ircle

Answer 66

lol

Answer 67

That's where a lot of people make mistakes, for an ellipse it's \[c^2 = a^2 - b^2\]

Answer 68

Note the negative sign

Answer 69

o.o gasp. that is no bueno.

Answer 70

b^2=a^2-c^2 then

Answer 71

:), now remember as I always say it's a game of substitution

Answer 72

\[b^2 = 16 - (2\sqrt{7})^2\]

Answer 73

\[b^2 = 16-28\]
\[b^2=-12\]

Answer 74

\[b=\sqrt{12}\]

Answer 75

No, the negative is there, something is wrong

Answer 76

Err, \[e = \frac{ c }{ a } \implies c = e \times a \implies c = \frac{ \sqrt{7} }{ 4 } \times 4 \implies \sqrt{7}\] bleh :)

Answer 77

..oh hehe

Answer 78

I guess I should be doing the math as well haha

Answer 79

sorry!

Answer 80

ai ai ai I need to go to bed soon. waay to early on a school night =.= and you do too.

Answer 81

No it's alright we just had mistaken the eccentricity we had sqrt(7)/2 when it's 4 :P

Answer 82

oh xD

Answer 83

Don't worry about me :), I'm the dark knight, night is where I work muahah!

Answer 84

right, right, how could I forget!

Answer 85

Alright so lets find b again bleh :)

Answer 86

\[b^2 = a^2-c^2\]

Answer 87

\[a = 4~~~c = \sqrt{7}\]

Answer 88

b = 3

Answer 89

b^2 = 9

Answer 90

Now that looks good

Answer 91

so..the answer I had at the very beginning. Look at the screenshot thing =.=

Answer 92

major axis runs vertically :P

Answer 93

ooh myy goooshh aspidghpaihgpi

Answer 94

fricken hour later hahahah

Answer 95

It's ok, the struggle is more important than the final answer, you will remember how to do it now :)

Answer 96

we're geniuses! :)