# Question:Monge(s circle of an ellipse

## Question:Monge(s circle of an ellipse

Maple 2021

This figure refuses to turn
Fig := proc(t) local a, b, P, Q, N, R, TG, x0, y0, p1, p2, p3, po, tp, sol; a := 11; b := 7; R := sqrt(a^2 + b^2); P := [R*sin(t), R*cos(t)]; x0 := P[1]; y0 := P[2]; TG := (a^2 - x0^2)*(y - y0)^2 + (b^2 - y0^2)*(x - x0)^2 + 2*y0*x0*(x - x0)*(y - y0) = 0; p1 := implicitplot(x^2/a^2 + y^2/b^2 - 1, x = -11 .. 11, y = -7 .. 7, color = blue); p2 := implicitplot(x^2 + y^2 - a^2 - b^2, x = -15 .. 15, y = -15 .. 15, color = blue); p3 := implicitplot(TG, x = -15 .. 15, y = -15 .. 15, color = red); sol := solve({x^2/a^2 + y^2/b^2 - 1 = 0, TG}, {x, y}, explicit); Q := [subs(sol[1], x), subs(sol[1], y)]; N := [subs(sol[2], x), subs(sol[2], y)]; po := plot([P, Q, N], style = point, symbolsize = 15, symbol = solidcircle, color = red); tp := textplot([[P[], "P"], [Q[], "Q"], [N[], "N"]], 'align' = {'above', 'left'}); display([p1, p2, p3, po, tp], scaling = constrained); end procnFig := 60;
Figs := seq(Fig(2*Pi*i/nFig), i = 0 .. nFig);
Error, (in Fig) invalid subscript selector
display(Figs, insequence = true);
NULL; Why this error message. Thank you.

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