v1:=y/(x^2+y^2-x):v2:=y/(x^2+y^2+x): v3:=simplify((v1+v2)/(1-v1*v2)); f:=unapply(v3,(x,y));# tan(Pi*(T-25/2)/100)=f(x,y) T:='T':c1:=T->cot(Pi*(T-25/2)/100); for j from 1 to 99 do p[j]:=plots[implicitplot](x^2+y^2-2*y*c1(j)=0,x=-20..20,y=-20..20): od: plots[display](seq(p[j],j=1..99),insequence=true); plot3d(f(x,y),x=-20..20,y=-20..20,axes=boxed);