SOLUTION: find the focus of x^2+4y^2+2x+24y++28=0

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Question 1086650: find the focus of x^2+4y^2+2x+24y++28=0
Answer by ikleyn(52803) About Me  (Show Source):
You can put this solution on YOUR website!
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find the focus of x^2+4y^2+2x+24y++28=0
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I don't know what "++" means; will assume that it is "+".

x%5E2%2B4y%5E2%2B2x%2B24y%2B28%7D%7D%5D+=+%7B%7B%7B0  ===> (I will complete the squares for x-terms and y-terms separately)  ====>  

x%5E2%2B4y%5E2%2B2x%2B24y = -28,

%28x%5E2+%2B+2x%29 + %284y%5E2+%2B+24y%29 = -28,

%28x%5E2+%2B+2x+%2B+1%29 + %28%282y%29%5E2+%2B+2%2A%282y%2A6%29+%2B+36%29 = -28+%2B+1+%2B+36,

%28x%2B1%29%5E2 + %282y%2B6%29%5E2 = 9,

%28x%2B1%29%5E2%2F3%5E2 + %28y%2B3%29%5E2%2F%283%2F2%29%5E2 = 1.






Ellipse %28x%2B1%29%5E2%2F3%5E2 + %28y%2B3%29%5E2%2F%283%2F2%29%5E2 = 1



The center of the ellipse is at (x,y) = (-1,-3).


The ellipse has the horizontal major axis.


The major semi-axis is 3 units long.


The minor semi-axis is 3%2F2 = 1.5 units long.


The linear eccentricity is sqrt%283%5E2+-+1.5%5E2%29 = sqrt%286.75%29.


The foci are at  (-1-sqrt%286.75%29,-3)  and  (-1%2Bsqrt%286.75%29,-3).

For more details, see the lessons
    - Ellipse definition, canonical equation, characteristic points and elements

    - General equation of an ellipse
    - Transform a general equation of an ellipse to the standard form by completing the square
    - Identify elements of an ellipse given by its general equation


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".