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Un tétraèdre est posé sur sa base  ACD.
Le point  P  appartient à l'arête  AB .
Le point  Q  appartient à la face  BCD .

Construire le point de percée de la droite  PQ
dans le plan  ACD .

La droite  PQ  est contenue dans le plan  BPQ
(plan auxiliaire).

La droite  BQ  coupe l'arête  DC  au point  R .

Le plan auxiliaire coupe donc
le plan  ACD  suivant la droite  AR .

La droite  PQ  rencontre
la droite  AR  au point  I .

Ce point  I  est le point de percée
de  PQ  dans  ACD  !

A = (-2.74, -0.46)
B = (0.52, 5.6000000000000005)
D = (2.32, -2.8000000000000003)
C = (6.1000000000000005, 1.08)
d = Segment(B, C)
e = Segment(C, D)
g = Segment(D, A)
h = Segment(A, B)
a = Segment(A, C)
P = Point(h)
Q = (2.5, 2.04)
b = Line(Q, P)
c = Line(B, Q)
R = Intersect(c, e)
i = Line(A, R)
I = Intersect(b, i)
I_1 = Point(b)
J = Point(b)
j = Segment(I_1, J)
k = 2.6 (slider from 0 to 50, step 0.1)
l = Ray(Q, I_1)
K = Point(l)
m = Segment(I_1, K)
poly1, q, p, k_2 = Polygon(P, B, Q)
poly2, a_1, p_1, q_1, g_1 = Polygon(A, P, Q, R)
f = Segment(B, D)
n = Ray(Q, I)
E = Point(n)
r = Ray(I, E)
s = Segment(Q, I)
F = (5.4, 4.36)
L = (4.22, -0.68)
u = Vector(F, L)
G = (13.42, 2.34)
M = (13.98, -1.34)
v = Vector(G, M)
N = (8.84, 0.26)
O = (7.640000000000001, -0.98)
w = Vector(N, O)
S = (2.3000000000000003, 5.7)
T = (1.32, 3.36)
z = Vector(S, T)
U = (2.7800000000000002, 5.68)
V = (1.82, 1.76)
t = Vector(U, V)
W = (5.5200000000000005, 4.4)
Z = (4.22, -0.62)
H = Point(r)
A_1 = Point(r)
b_1 = Segment(H, A_1)
B_1 = Point(c)
c_1 = Ray(R, B_1)
C_1 = Point(c)
d_1 = Ray(B, C_1)