Réponse :
1) A = (AC*AB)/2
A =(3*4)/2 = 6cm²
2) A = (base*h)/2
A =(BC*AK)/2
on connait l'aire
on calcule la base
BC²=AC²+AB²
BC²= 9²+4²
BC=5cm
on calcule AK
6 =(5*AK)/2
6*2 =5AK
AK = 12/5=2,4cm
c)ACK rectangle en K
CK²=CA²-AK²
CK²=3²-2,4²
CK=√3,24=1,8cm
BK = BC-CK
BK = 5-1,8=3,2cm