\documentclass{standalone} \usepackage{luamplib} \begin{document} \mplibtextextlabel{enable} \begin{mplibcode} vardef invert(expr P, C) = save o; pair o; o = 1/2[point 0 of C, point 4 of C]; save r; numeric r; r = abs (point 0 of C - o); save s; numeric s; s = abs (P - o); o + (P - o) * r / s * r / s enddef; beginfig(1); path C, L; numeric r; r = 89; C = fullcircle scaled 2r; L = (up--down) scaled 120 shifted 184 right rotated 38; pair a, b, o; a = point 0 of L; b = point 1 of L; o = center C; pair P, Q, R, P', m; P = whatever[a, b]; o - P = whatever * (a - b) rotated 90; Q = C intersectionpoint halfcircle zscaled (P-o) shifted 1/2[P, o]; R = C intersectionpoint halfcircle zscaled (o-P) shifted 1/2[P, o]; P' = whatever[o, P] = whatever [Q, R]; draw subpath (-3.5,3.5) of fullcircle zscaled (P'-o) shifted 1/2[o, P'] dashed withdots scaled 1/4 withcolor 1/3 blue; draw unitsquare scaled 5 rotated (270 + angle (P-Q)) shifted Q withcolor 3/4 white; draw unitsquare scaled 5 rotated (90 + angle (P-o)) shifted P withcolor 3/4 white; draw unitsquare scaled 5 rotated (90 + angle (P-o)) shifted P' withcolor 3/4 white; draw P -- Q -- o -- R -- cycle withcolor 1/2 white; draw Q--R; draw o -- P; draw L withcolor 2/3 blue; draw C dashed evenly scaled 1/2 withcolor 1/2[2/3 blue, white]; dotlabel.top("$Q$", Q); dotlabel.lrt("$R$", R); dotlabel.urt("$P$", P); dotlabel.llft("$O$", o); fill fullcircle scaled 3/4 dotlabeldiam shifted o withcolor white; label.lft("$r$", 1/2[o, Q]); drawdot P' withpen pencircle scaled dotlabeldiam; label("$P'$", P' shifted 10 dir 68) withcolor 2/3 blue; drawoptions(withcolor 2/3 blue); label.bot("\textit{circle of inversion}", point 6 of C); label.top(TEX("\textit{polar}") rotated angle direction 0 of L, point 1/4 of L); z0 = P' + 20 dir -20; draw z0 -- P' cutafter fullcircle scaled 8 shifted P' withpen pencircle scaled 1/4; label.rt("\textit{pole}", z0); drawoptions(withpen pencircle scaled 2 withcolor 2/3 blue); for i = 1/8, 1/4, 3/8, 5/8, 3/4, 7/8: draw point i of L; draw invert(point i of L, C); endfor drawoptions(); label("$\displaystyle {r\over OP} = {OP' \over r}$", 1/2[point 0 of C, point 1 of L] + 12 down); label("$\displaystyle r^2 = OP \times OP'$", 1/2[point 0 of C, point 1 of L] + 36 down); endfig; \end{mplibcode} \end{document}