SOLUTION: what is the equation of the ellipse with foci at (0,-4)and (0,4)and the sum of its focal radii being 10

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Question 42917: what is the equation of the ellipse with foci at (0,-4)and (0,4)and the sum of its focal radii being 10
Answer by fractalier(6550) About Me  (Show Source):
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If the sum of the focal radii is 10, we know b = 5. And if the foci are at (0, ±4), we know c = 4. Then a^2 = b^2 - c^2 = 25 - 16 = 9 and a = 3.
Thus our equation is
x^2 / 9 + y^2 / 25 = 1