Missing

\title{Propriété de Thalès dans un triangle isocèle}
\language{fr}
\range{-5..5}
\author{Odile Bénassy}
\email{obenassy@free.fr}
\computeanswer{no}
\format{html}
\precision{10000}

\matrix{f1=
9,3,2,6
12,4,3,9
15,5,4,12
18,6,4,12}
\text{fa=randomrow(\f1)}
\text{a=item(1,\fa)}
\text{b=item(2,\fa)}
\text{c=item(3,\fa)}
\text{d=item(4,\fa)}
\matrix{f2=
8,4,3,6
10,5,4,8
12,6,5,10
14,7,6,12}
\text{fb=randomrow(\f2)}
\text{e=item(1,\fb)}
\text{f=item(2,\fb)}
\text{g=item(3,\fb)}
\text{h=item(4,\fb)}
\matrix{f3=
9,6,4,6
12,8,6,9
15,10,8,12
18,12,10,15}
\text{fc=randomrow(\f3)}
\text{i=item(1,\fc)}
\text{j=item(2,\fc)}
\text{k=item(3,\fc)}
\text{l=item(4,\fc)}
\matrix{seg=
-4,5,4,5,-6,7,5,7,\a,\b,\c,\d
-6,0,6,0,-8,2,7,2,\e,\f,\g,\h
-8,-5,8,-5,-10,-3,9,-3,\i,\j,\k,\l}
\text{col=randomrow(\seg)}
\text{l1=item(1,\col)}
\text{l2=item(2,\col)}
\text{l3=item(3,\col)}
\text{l4=item(4,\col)}
\text{l5=item(5,\col)}
\text{l6=item(6,\col)}
\text{l7=item(7,\col)}
\text{l8=item(8,\col)}
\integer{l9=item(9,\col)}
\integer{l10=item(10,\col)}
\integer{l11=item(11,\col)}
\integer{l12=item(12,\col)}

\statement{<p><center>
\draw{200,200}{
xrange -20,20
yrange -20,20
triangle 0,15,-12,-15,12,-15,black
line -12,-15,12,-15,red
line \l1,\l2,\l3,\l4,red
text black,-0.5,17.5,medium,A
text black,-13.5,-15,medium,B
text black,12.5,-15,medium,C
text black,\l5,\l6,medium,M
text black,\l7,\l8,medium,N
}
</center> <p>
[MN] // [BC] ; AB = \l9 cm ; AM = \l10 cm ; MN = \l11 cm. Combien  
mesure [BC] (en cm) ?}

\answer{Longueur de BC}{\l12}