Math CentralQuandaries & Queries


Question from Brad, a student:

I am trying to figure out how to find the foci of an ellipse x^2/7 + y^2/16 = 1.

Since 16 is the largest denominator I know the major axis is going to be the y axis.

Do I now take 7-c^2=16. c^2=16-7, c^2=9, c=3. So are my foci (0,+-3).

Hi Brad,

Yes, the foci are (0, 3) and (0, -3).


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