# Elliptic trigonometry

Why aren't there trigonometric functions for elliptic geometry? There is trigonometry for circles and hyperbolas, but why not ellipses?

tiny-tim
Homework Helper
Hi JyN!
There is trigonometry for circles and hyperbolas, but why not ellipses?

ah, there is trigonometry only for the square hyperbola (ie with perpendicular asymptotes), just as there is only for the "square" ellipse (ie the circle).

Why can't trigonometry-like relationships exist for non-square hyperbolas and ellipses?

tiny-tim
Homework Helper
i expect they can be, but why would anyone bother with them, when the "square" functions can easily be adapted for the purpose?

An angle in radians is defined as the length of the arc of a circle over its radius.

A slight problem occurs if you want to extend that to an ellipse because an ellipse is defined by two variables, major axis and minor axis. It would be interesting how to define an elliptic angle, length of arc of an ellipse over major axis or minor axis or their algebraic combination? But in either case, I don't know how this could be useful other than perhaps in an elliptical coordinate system.

Petek
Gold Member
Why aren't there trigonometric functions for elliptic geometry? There is trigonometry for circles and hyperbolas, but why not ellipses?

Is this what you had in mind? They're called Jacobi elliptic functions.

EDIT: Cross post!