1) 180 - 120 = 60°
cos 60 = adjacent/hypoténuse = BH/AB
BH= AB cos 60 = 6 * 0,5 = 3cm
2)AH² = AB² + BH² = 6² + 3² = 36 + 9 = 45
[tex] AH = \sqrt{45} = 3\sqrt{5}\\\\Aire = (13*3\sqrt{5})/2 - (3*3\sqrt{5})/2\\ =[(39 - 9)\sqrt{5}]/2 = (30\sqrt{5})/2 = 15\sqrt{5} cm^2 [/tex]
En espérant t'avoir aidé.
