Perimeter of an ellipse from radii, and vice-versa

Hi there,

I'm new here. Greetings. I just posted this in the pre-Calculus forum but realize I should put it here, so....

I need to figure out how to calculate the perimeter, or circumference, of an ellipse using the radii, and vice-versa: how to figure out the radii given the perimeter and the __ratio__ of the two radii to each other.

I found an equation for the perimeter, or circumference here: Circumference/Perimeter of an Ellipse: Formula(s) - Numericana)

given the radii x and y, where x>y:

P=3.1415*(((2*((x^2)+(y^2)))-(((x-y)^2)/2))^.5)

The result will be an approximation but it will be close enough.

Any chance you could help me solve this equation for x in terms of C and y, and then also for y in terms of C and x?

I’m pretty rusty on my equations!

Many Thanks,

rgesh

San Francisco, CA

Re: Perimeter of an ellipse from radii, and vice-versa

Please don't post the same question in multiple areas. This is asked and nswered here: http://mathhelpforum.com/pre-calculu...ice-versa.html