Question

What are co-vertices in r/o an ellipse?

Answer 1

Co-vertices are the endpoints of the minor axis .

Explanation:

Co-vertices are the endpoints of the minor axis .

Let us consider an ellipse described by `x^2/16+y^2/9=1`. This is shown below:
graph{x^2/16+y^2/9=1 [-10, 10, -5, 5]}
This is an ellipse with horizontal orientation and as can be seen its co-vertices are `(0,3)` and `(0,-3)`.

Now consider another ellipse `(x+3)^2/9+(y-4)^2/25=1`
graph{(x+3)^2/9+(y-4)^2/25=1 [-12.34, 7.66, -1, 9]}
This is an ellipse with vertical orientation and as can be seen its co-vertices are `(-6,4)` and `(0,4)`.