Find An Equation Of The Ellipse Having The Given Points As Foci And The Given Sum Of The Focal Radii (-9, 0); (9, 0); 30?

The semi-major axis will be (30 - (9-(-9)))/2 + 9 = 15 units long. The semi-minor axis will be √((30/2)^2 - 9^2) = 12 units long. The center is located at (0, 0) An equation is  (x/15)^2 + (y/12)^2 = 1

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Check   We expect points (-15, 0) and (0, 12) to be on the ellipse.   (-15/15)^2 + (0/12)^2 = 1    (yes)   (0/15)^2 + (12/12)^2 = 1    (yes)