Fichier fg-v8_61-62.mp (figure 1) — Modifié le 4 Avril 2008 à 00 h 23

Construction d'un pentagone

fg-v8_61-62.mp (figure 1)
Le point G divise le segment [A,B] selon le nombre d'or. Quatre cercles de même rayon AB suffisent alors à déterminer les sommets d'un pentagone.
Source


picture UnBeauPoint;
UnBeauPoint := image(
    fill fullcircle scaled 3pt;
    fill fullcircle scaled 2pt withcolor red+green;
);

vardef pointe expr p = draw UnBeauPoint shifted p; enddef;
     


pair A,B,G,P[];
path C[];

UnSurPhi = (sqrt(5) - 1) / 2;


beginfig(1);
    A := origin;
    B := right scaled 3cm;
    G := UnSurPhi [A,B];
    
    C1 := fullcircle scaled (2 abs(B-A)) shifted A;
    C2 := C1 shifted (B - A);
    C4 := C1 shifted (G - A);
    
    P1 := G + B - A;
    
    C5 := C1 shifted (P1 - A);
    
    P2 := C1 intersectionpoint C5;
    P4 := (reverse C1) intersectionpoint C4;
    P5 := (reverse C2) intersectionpoint C5;
    
    fill (A--P4--P5--P1--P2--cycle) withcolor (.9,.7,.65);
    draw A--P4--P5--P1--P2--cycle;
    
    draw A--P1;
    draw C1;
    draw C2;
    draw C4;
    draw C5;
    
    draw P2--P4 dashed evenly
	withcolor (0.2,0.3,0.6);
    
    pointe A;
    pointe B;
    pointe G;
    pointe P1;
    pointe P2;
    pointe P4;
    pointe P5;
    
    label.llft(btex $A$ etex, A);
    label.llft(btex $G$ etex, G);
    label.lrt(btex $B$ etex, B);
    label.lrt(btex $P_1$ etex, P1);
    label.top(btex $P_2$ etex, P2);
    label.llft(btex $P_4$ etex, P4);
    label.lrt(btex $P_5$ etex, P5);
    
endfig;

end