Toán Lớp 9: cho ΔABC; AB=8cm, AC= 12cm; ∠A= 30 $^{0}$ . Tính $S_{ABC}$
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Toán Lớp 9: cho ΔABC; AB=8cm, AC= 12cm; ∠A= 30 $^{0}$ . Tính $S_{ABC}$
Comments ( 2 )
Kẻ BH _I_ AC
Xét ∆HBA vuông tại H ta có :
+) sinA = sin30° = HB/AB = HB/8
=> HB = 8*sin30° = 8*½ = 4 (cm)
Xét ∆ABC , BH đường cao ta có :
+) Sabc = (BH*AC)/2 = (4*12)/2 = 24 (cm²)