Hello,(adsbygoogle = window.adsbygoogle || []).push({});

given (x^2)/(a^2) + (y^2)/(b^2) = 1.

and using polar coordinates x=rcos(phi) , y=rsin(phi),

equating gives r^2 = 1/[(cos^2(phi)/a^2) + (sin^2(phi)/b^2)].

or if we leave b in the nominator :

r= b/[(sin^2(phi)+(b^2/a^2)cos^2(phi)]^1/2.

-could someone give a hint as to how the demoninator of the last expression can be turned into [1 - (e^2)cos^2(phi)]^1/2 where e is the eccentricity of the ellipse?

and what is the value of e?

thank you.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: The radius of an ellipse from the origin.

**Physics Forums | Science Articles, Homework Help, Discussion**