Dorothy was asked to write the equation of the ellipse [centered at the origin] with Foci (+25,0) and sum of focal radii 60. Follow her work below to identify her mistake, explain why it is wrong, and then show/tell Dorothy how to find the correct equation. Dorothy's work/explanation: The Foci tell me that c = 25. The sum of the focal radii tell me that a = 30 and that the Major Axis is horizontal. Since (25)2 + (30)² = 625 + 900 = 1525, my equation is: 900 + 1525 =1.