Is it possible to work out the centre of an ellipse?

[Focus]

Is it possible to work out the centre of an ellipse?
The question asks for the eccentric angle of the ellipse with the equation x²+9y²=13 at point (2,1)...
I have no idea how to get this, I know that the angle would be arctan(1/2) if the ellipse was centred at (0,0)

Thanks

 

[Kamataat]

But the ellipse IS centered at the origin. It asks for the eccentric angle between the x-axis and the line joining (0,0) and (2,1).

edit: PS: The eccentric angle is not simply arctan(y/x), you have to take the axes of the ellipse into account too!

- Kamataat

 

[Focus]

But the ellipse IS centered at the origin. It asks for the eccentric angle between the x-axis and the line joining (0,0) and (2,1).

edit: PS: The eccentric angle is not simply arctan(y/x), you have to take the axes of the ellipse into account too!

- Kamataat

I am somewhat confused. Surely the line joining (0,0) and (2,1) makes arctan (.5) of an angle with the x axis.

 

[Kamataat]

Look at this: http://mathworld.wolfram.com/EccentricAngle.html

- Kamataat

 

[Focus]

Thanks a lot