I want to figure out the 'a' of an ellipse (i.e. (major axis)/2) by knowledge of it's circumference and length of minor axis. Using my little knowledge which I gained from reading (roughly) the ellipse article of wikipedia; I realized that I need to use that notorious and approximate circumference formula...so I made an equation to derive the 'a' or half of the major axis which needs to be solved. quickmath.com gave 4 results so as to turn my vertical scroll bar into a tiny line (try it yourself, I'll post the equation). Axiom suggest a syntax error which I know it not true, I think it has given up. This is the equation - h=((22/7)*(x+(c/2))*(1+(((3*((x-(c/2))/(x+(c/2)))^2))/(10+(4-(3*((x-(c/2))/(x+(c/2)))^2))^(1/2)))))/2 Which obviously I've converted from human readable format. You need to solve for x to get the major axis.