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