I'm revising form my A-levels now and I ran into a bit of problem with a question. It looks easy, but I can't get the answer at the back of the book. Could be a typo, but could be me that's wrong. Question: The eccentric angle corresponding to the point (2, 1) on the ellipse with equation [tex] x^2 + 9y^2 = 13[/tex] is [tex]\theta[/tex]. Find [tex]\tan \theta[/tex] The book isn't very clear on what the eccentric angle is, so could someone maybe explain that to me, please? I understand it as the angle from the middle of the ellipse - in this case the origin - to the point (2, 1). So, [tex]\tan \theta[/tex] would be opposite/adjacent, 1/2. Apparently, it's not.