We plot the 2 vertices and the 2 co-vertices: 



We sketch in the graph of the ellipse:



The equation of an ellipse with center (0,0) which has its major
axis vertical is

x²   y²
—— + —— = 1
b²   a²

Where "a" represents the number of units from the center 
to either of it vertices and "b" represents the number of
units from the center to either of its co-vertices.  So
a = 5 and b = 3 and the equation is:

x²   y²
—— + —— = 1
3²   5²

or

x²   y²
—— + —— = 1
9    25

Edwin