The standard for of an ellipse is:
(x-h)²/a² + (y-k)²/b² = 1, where h and k are the coordinate of its center.
Since its center is at the origin, then the formula becomes:
x²/a² = y²/b² = 1
The vertex being at (9,0) then a = 9
The co-vertex being at (0.1). then b =1
Hence, the final equation:
x²/9² + y²/1² = 1
x²/81 + y²/1 = 1 ↔ x²/81 + y² = 1 (1st answer)