Hello, 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.