Conics in polar form

[f1player]

Find an equation for the elliptical orbit of the earth about the sun (at one focus) given an eccentricity of 0.017 and a major axis of 2.99 * 10^8 km.

The answer given is r = (1.49 * 10^8)/(1-0.017cos@)

I'm not sure how to use the value for the major axis, since r = ek/(1-ecos@). There's nothing ther about the major axis, only eccentricity and directrix.

 

[tkhunny]

Are you aware of these:

Distance between foci is 2*a*e

Length of semi-latus rectum, l, is related to given parts

a*l = b^2 or l = a*(1-e^2)

 

[f1player]

I wasn't aware of those, however I still don't understand the reasoning behind the two equations you gave.