bonjour,
triangle rectangle ABC
angles(A+B+C)=180°
angles (A+90°+60°)=180°
angle A=180-(90+60)
angle A=180-150
angle A=30°
1)
AH
triangle rectangle ABH
cosA=AH/AB
cos 30°=AH/8
0.86=AH/8
AH=6.88
AH=6.9
2)
HC
triangle BHC
tangente C=BH/HC
tgt 60°=4/HC
1.73=4/HC
HC=4/1.73
HC=2.3
3) AK
AC=AH+HC
AC=6.9+2.3
AC=9.2
triangle ABC
JK//BC
d'où
AJ/AB=AK/AC
2/8=AK/9.2
1/4=AK/9.2
AK=9.2/4
AK=2.3
