Foci of an ellipse | Conic sections | Algebra II | Khan Academy
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Calculating the foci (or focuses) of an Ellipse.
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I translated this video in Korean :)
제가 번역했어요 :)
btw, this is the law of planetary motion that Kepler used to prove that the earth revolved around the sun.
A fancy way of telling spin is preserved
Wow 12 years comment
ASTRONOMY OLYMIAD FTW!!!!!!!!
thank you so much i was sick from school, and i bet this is better than what i would have learned!
It finally makes sense! Thank you :)
can you do a video on the proof of the foca/optical property!!
Thank you so fucking much I couldn't understand foci... ._.
Now this is where I get confused. So when you say that F1 + F2 = 2A, do you actually mean F1 + F2 = major diameter? Because things gets messy when the ellipse stands upright (B > A). Because in that case, the variable "A" in the equation is representative of the minor radius, but does the equation F1 + F2 = 2A still stand? Or do you actually mean F1 + F2 = major diameter and things just got confusing because we keep using the same variables.
I know this is 3 years later but yes, F1 + F2 = major diameter as far as I understand.
If b was bigger than a, then the focal points would just lie on the vertical axis
@@animationcity8178thanks man, I can finally finish my homework 3 years later
@@midori58 happy to help buddy
Question
If the major axis was parallel with the y-axis where going to add and subtract the y-value?
Thanks as always...if u could pls do a video on conjugate diameter of ellipse. It will b big help.
I see a lot of comments asking what if the ellipse is tall and skinny (or if a and b are switched). It's really the same thing if you think about it; it's just a 90-degree rotation of the one shown in the video. I think a and b would just be switched in the formulas (I'm not sure though).
thanks a lot salman sir......u made things so easy for me.....thanks once again
well, if you have the co-vertices you know the minor axis, because they are the shortest points from the center of the ellipse. with the focus you can work backwards to find the major axis. With that you can derive the standard equation, given you know where the origin is.
This is Amazing. The best TH-cam channel on earth.
isn't the last scene's left focus'coordinate be（-1-√5,-2）???if I'm wrong,please correct me...
very helpfull for my investigation
OMG thanks u sooooo much!!! u r a genius!!!
Thanks. My final Extension maths exam is in 3 days and this helped heaps!
Ryan Park yes I passed 8 years ago 😂
Great 🎉😂
i think you can give a donation to the academy ;)
These videos have been helpful to me, as I'm developing my string theory. :D
scientists are dealing with mathematics that aren't even taught in school, or on youtube videos (the cutting edge), that deal with string theory, i doubt u'd develop it. Plus there already is a current theory for string theory that TON's of mathematicians and scientists worked on. And if that doesn't cut it, it's most likely something we didn't discover yet that's stopping it. But knock yourself out.
Why say that before looking into it?
The Processionist wow, i just told you. But knock yourself out, not trying to stop you, i was just informing you in case you weren't already.
No harm done. You might take a look at my model and find me on facebook. Start fresh and check it out. :D
@@theprocessionist6442 have you solved it yet?
U are a really great techer
You r great sir, 🙏🙏🙏
Is "a" always the semi major radius, for example if you switch the denominators 9 and 4(vertical ellipse), would "a" still be 3 or would it be 2?
so pumped for the math test tomorrow!
was it useful after 7 years?
@@x15cyberrush9 9
@@kimothefungenuis yea time flies
But why does d1 + d2 = constant at the first place ?
abdou amaadour its a property of ellipse. just like radius of circle is always constant for every point on the circle
Why are you what you are?
Definition of ellipse.
why is the center (1,-2) ?????
You should post an example with meters not invisible numbers it difficult to understand.
this video saved my math quiz score :))
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Ty
honestly how many more times can you say d1 + d2 = 2a
Wonderulllll.
Thank uuuuuu
İn 13.05 √5 is equal to 2.23 and focus (3.23,-2) but this point is not in the elips
Ia focus doesn't have to be on the ellipse
Are the foci always symmetrical?
Sally Chan compared to the center, yes.
G+H is the same as G+H
Thanks for the explanation
Sal what do you get out of this? I mean superman gets lois lane batman gets a cool car what do you get for saving millions of children's futures
lol...back when youtube used the stars
how can you get the value of "d" instead of not knowing any information about focus? IS there any defined structure for this? I am too much confused rather than being helped.
it's so messed up
I think this is the best TH-cam channel where we can learn for free!
Keep it up Khan Academy 👍🏻
DONT FALL FOR THIS! INSTAPORTAL IS A SCAM THAT STEALS YOUR MONEY AND DOESNT ACTUALLY WORK. ALSO HACKING PEOPLES ACCOUNTS IS ILLEGAL WITHOUT CONSENT!
balls
how do you find the coordinates of an ellipses focus when you don't know any information about the equation.
This comment section is as old as time.
I have a crush on math.
Thank you Khan academy😊😊😊.
I HEARD A DOG IN THE BACK GROUND O.O at 8:12
And then everything clicks…
Yeo Wool don't you just love that
I swear. I've got a major exam in 7 days and I've been trying to get my head around conics for the last 3 days and now I watch this and it all seems so easy.
Thank u so much ....
isn't the last scene's left focus'coordinate should be（-1-√5,-2）???if I'm wrong,please correct me...
Daria wicgs No. You are subtracting sqrt5 from the origin. The origin is at 1
An ellipsis goes to circle when ditanance between focies goes to zero
you may have just saved me from failing my test on monday! Thank you so much!
how did it go
@@smf5769 dude its been 10 years haha. he/she probably passed by now.
Nah idts, they're not responding cos they failed
i want an update
Wasn't expecting to see this on a 10 year old post BUT I passed, went to college, and got a good job. This video definitely helped.
wow... almost 10 years ago now
How can we prove that the sum of the distances from any point to the foci stay constant?
So helpful!
It's good but I can't understand the concept of foci
Loved it.
THANK YOU!!!!!!!!!! UR AWESOME!!!
I'm a teacher and I am very interested in what program you are using to make this video. I thank you in advance.
Hi Kentaro!
thank you so much.... i finally understand ellipses now!
Really interesting video thanks alot great explanations.
Thanks
Anyone from Aviation here? ;D
My teacher sent me here
What if they give me the co-vertices and the foci and ask to write the standard equation?
Hihi, great thanks. I have a question: Can I find a Foci if I only have major axis and one point on the ellipse.
Preparing for my second semester exams in 4 days. Great video
very nice video and content has been explainrd very beautifully
You are amaaaaaaaaaazing .. Thanks SoOoOo much
That was very helpful .. Keep going ;)
Fosi sounds wierd, I pronounce it Foki, afterall you don't say fosus in singular form. Great vid though..
Thx alot! BTW Is a vertical shaped ellipse different? How would you find the coordinates of the foci of that?
Another great explanation! Excellent.
show graph of everything in ellipse so we find out actual position of foci ???
THANK YOU SO MUCH!!!!! Very helpful thanks man.
what software is he using to draw this stuff?
Nice, it would be cool if you discussed on Kepler's laws of planetary motion with this!
thanks.. this really helps!!!!!!!
yeah you should >:(((( jkjkjkjk
Khan Academy is much better than my school
Hey Marvin's Analytic Geometry Class!
thx..... very happy with this
I don't understand, why do you have to say "(one plus the square root of 5, -2)"? When finding the vertices(of the major axis), shouldn't you just be able to count, in this case, plus or minus two along the x-axis from the center of the ellipse? Thus, making the vertices of this ellipse (3, -2) & (-1, -2)? Why the square root of 5? Why add the foci if it just represents a point of focus for each parabola???
Why ellipse has two focus?
no he doesn't
At 5:57 he says the minor radius is a. Isn't a the major radius?
Rupali yep
I am here in sep 2021
That was great. Thank you!
Chhichha leather kar diya tune.
Is f is half of a
I think you're wrong when you say a>b means that it's horizontal. it's horizontal if the x value is over the a value, and not the y value
no sound
Good
NOOOOO, DON'T USE H AS A DISTANCE LIKE THAT IT HURTS MY BRAIN!!! USE A DIFFERENT LETTER!!!!!
Well you didn't prove that the sum is true for any point on the ellipse though...
In the example, a is actually 3, and b is actually 2. Right? Also, would be nice to prove f=2a, as someone else has suggested.
This video doesn't quite explain how the equation F1 + F2 = 2a. Could anyone help me with that?
The spider in your avatar is the first little gag like that I've fell for in a while
what's the proof of d1 + d2 = 2a.. please explain
He made a video about it, check the conic sections playlist
Could you please tell us the title? Or pass a link?
It's in this very same video th-cam.com/video/QR2vxfwiHAU/w-d-xo.html
From the definition of an ellipse: the sum of distances from focii (focuses) is a *constant.* Then we pick a point from an ellipse, that is also on a major axis. Hence the sum of distances from foci, is the length of a major axis. And since *a* is half of major axis, the distance is *2a.* Since the sum of distances from foci to any point on ellipse is a constant, and we know that distance in on special case (when we pick a point that's on a major axis), then we know that what ever d1 and d2 are, the sum d1 + d2 = 2a.
the 7 people who disliked this are teachers that don't know how to teach :D
can you do a video on the proof of the Focal/Optical Property for ellipses, thanks
average of 4.5 stars... wtf who didnt give 5 to this guy wtf
7 questions kho kho answer plz