SOLUTION: Write an equation for the ellipse, satisfying the following conditions. Foci at (0,-2) and (0,2); the point (3,2) on the ellipse

Algebra.Com
Question 1082287: Write an equation for the ellipse, satisfying the following conditions. Foci at (0,-2) and (0,2); the point (3,2) on the ellipse
Found 2 solutions by natolino_2017, ikleyn:
Answer by natolino_2017(77)   (Show Source): You can put this solution on YOUR website!
The mid point between the two focus is the center of the ellipse.
In this case, Center= ((0+0)/2 , (2+-2)/2) =(0 , 0).
Let P = (3 , 2), F1 = (0 , -2), F2 =(0 , 2)
"The sum of the distance of a point of the ellipse to every Focus, is constant and equal to the double of the Semi-major axis (A)"
PF1 + PF2 = 2A.
5 + 3 = 2A
A = 4
Let C: distance from the center to a focus.
C = 2.
A^2 = B^2 + C^2
B = sqrt(12).
So the equation is
x^2/12 + y^2/16 = 1.
observation: the Focus doesn't belong to the ellipse.
@natolino_

Answer by ikleyn(52803)   (Show Source): You can put this solution on YOUR website!
.
1.  The center of the ellipse is at (0,0).

    The major axis        is y-axis x= 0;
    Hence, the minor axis is x-axis y= 0.


2.  The canonical equation of this ellipse is 

     = 1    (it is written in the form to fit the fact that the major axis is y-axis: a > b > 0)

    Since the point (3,2) is on the ellipse, it implies 

     = 1,   or

     = .    (1)


3.  The focal distance is 2c = 2 - (-2) = 4.
    Hence, the linear eccentricity c =  = 2. It means that

     = 4.          (2)


4.  Thus you have two equations (1) and (2) to determine "a" and "b".

    You can simplify writing and solving by introducing new variables x =  and y = :

    9x + 4y = xy         (3)     instead of (1), and
    x - y = 4.           (4)     instead of (2)

The setup is done.
Now it is simple arithmetic to solve it and to get "a" and "b" at the end.


4.  From (4), x = 4 + y, Substitute it into (3). You will get

    9(4+y) + 4y = (4+y)*y,

    36 + 9y + 4y = 4y + y^2  --->  y^2 -9y - 36 = 0  ---->   =  = .

    Only positive root works: y = 12.  So,  = 12 and b = .

    Then a^2 = b^2 + 4 = 12 + 4 = 16 and  a =  = 4.

    Thus semi-axes are  4 (vertical) and  (horizontal).


    The equation for the ellipse is

     +  = 1.


As a prerequisite, see the lesson
    - Ellipse definition, canonical equation, characteristic points and elements
in this site.


Also,  you have this free of charge online textbook in ALGEBRA-II in this site
    ALGEBRA-II - YOUR ONLINE TEXTBOOK.

The referred lesson is the part of this online textbook under the topic
"Conic sections: Ellipses. Definition, major elements and properties. Solved problems".



RELATED QUESTIONS

Write an equation for the ellipse, satisfying the following conditions. Foci at (0,-2)... (answered by josgarithmetic,lwsshak3)
Write An equation for each ellipse. Foci at (-3, -3), (7, -3); the point (2, -7) on... (answered by greenestamps)
Write An equation for each ellipse. Foci at (-3, -3), (7, -3); the point (2, -7) on... (answered by ikleyn)
Write an equation of an ellipse centered at the origin, satisfying the given conditions. (answered by lwsshak3)
Write an equation for the ellipse Eccentricity 3/4; foci (0,-2)... (answered by lwsshak3)
find the standard form of the equation of the ellipse satisfying the given conditions.... (answered by lwsshak3)
Write an equation of the ellipse with foci (0,+2)|(0,-2) and co-vertices at... (answered by lwsshak3)
Find an equation for the conic that satisfies the given conditions. Ellipse foci (0,... (answered by lwsshak3)
The foci of an ellipse are (-3,-6) and (-3,2). For any point on the ellipse, the sum of... (answered by ikleyn)