>I?am?starting?to?learn?maxima.?The?best?is?to?do?by?examples.?So?I >have?those?equations: > >eq1:x^2/a^2+y^2/b^2=1; >eq2:A(x-x0)+B(y-y0)=0; In eq2, I think you need A*(x-x0)+B*(y-y0)=0, not A(x-x0)+B(y-y0)=0. The expression A(x-x0) means function A evaluated at x - x0. --Barton