
Nick S. answered 06/01/20
Experienced and Proven Calculus, Astronomy, and Physics Tutor.
The equation of an ellipse is (x-h)2/a2 + (x-k)2/b2 = 1 . The point (h,k) is the center of the ellipse. In this case (h,k) = (0,0) because the ellipse is centered at the origin.
The value 'a' can be either the distance from the center to the vertex or from the center to the co-vertex. It depends on which one is displaced in the x-direction because 'a' is in the denominator of the x term. In that case 'a' is 5 because the vertex is displaced horizontally by 5 from the center. Under that same logic b is 4 because the co-vertex is displaced vertically from center by a distance of 4.
Sub all the values in and you will have your equation.