1. the perimeter of △ABC is 21cm.
(a)Find BC
(b)Find ∠BAC
(c)Find the ares of △ABC
請問有沒有識這條數學呀....help
2007-12-06 7:20 pm
回答 (1)
2007-12-06 10:39 pm
✔ 最佳答案
1)x=perimeter-AC-AB=21-5-9
=7
2)by using cosine rule
x^2=AB^2+AC^2-2AB．ACcosQ
7^2=5^2+9^2-2(5)(9)cosQ
cosQ=0.633
∠BAC=50.7 degrees
c)
AREA=底Ｘ高／２
=(AC)(ABsin∠BAC)/2
=9x5xsin(50.7)/2=17.4
收錄日期: 2021-04-11 16:21:34
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