Write the equation of an ellipse given the center vertex and focus

How do you determine whether the major axis of an ellipse is horizontal or vertical?

Given the center at (0,0) and a vertex at (5,0), how would you write the equation of the ellipse?

What is the relationship between the distance from the center to the focus and the distance from the center to the vertex in an ellipse?

What is the formula that relates C, A, and B in the context of an ellipse?

How do you calculate B squared if you know A squared and C squared?