Register to reply 
Ellipse through three points 
Share this thread: 
#1
Jul511, 07:04 AM

P: 6

1. The problem statement, all variables and given/known data
First of all, I'm not sure the following is achievable at my level (last year of high school), as it is not posed as a direct question, but if yes, could you point me in the right direction? I'm trying to find an ellipse that goes through three points, (0,0) , (b,0) and (b/2,h). This actually represents a building with a base of width b and a height of h. The building is symmetrical, therefore the ellipse is not 'rotated' (I'm not sure how to express this mathematically). 3. The attempt at a solution Using the equation for an ellipse (not trying to confuse anyone but h is not H and b is not B): (((XH)^2)/(A^2)) + (((YK)^2)/(B^2)), I find the following (using logic and no algebra): H is b/2 as the centre of the ellipse always goes through the line x=b/2 A is greater than or equal to b/2. (otherwise the ellipse cannot touch both points on the x axis) B is greater than or equal to h. (I don't want the building to have angles greater than 90^{o}) Using the above statement, I expressed B as h + C and found that K = C. I realise there is an infinite number of ellipses (at least I'm assuming so), but I think that A should be dependent on b, h and/or C. Could you help me find this? Thank you for your help. EDIT: OK, I think I found my answer by replacing A by b/2 + D, plugged in x=0, y=0 then I rearranged until it looked like a quadratic equation with D as the 'variable' and I got an answer for D in terms of b, h and D. Sorry for making a new topic . 


Register to reply 
Related Discussions  
Calculate ellipse from 4 points?  Differential Geometry  4  
Build an ellipse given 3 points and the focus  General Math  8  
Ellipse given n minimum points and knowing one of the focus  General Math  0  
3d ellipse given two points  Differential Geometry  1  
Points on an ellipse  Calculus & Beyond Homework  4 