in triangle ABC,
a+b : b+c : c+a= 15:11:13
a：b：c=17：13：9
cos A : cos B: cos C = ?:?:?
the largest angle of trianagle ABC
sin cos tan
2012-03-18 9:00 pm
回答 (1)
2012-03-18 9:20 pm
✔ 最佳答案
a : b : c = 17 : 13 : 9Let a = 17k, b = 13k, c = 9k
cosA = (b^2 + c^2 - a^2)/(2bc) = -39/234 = -17/102
cosB = (a^2 + c^2 - b^2)/(2ac) = 201/306 = 67/102
cosC = (a^2 + b^2 - c^2)/(2ab) = 377/442 = 87/102
So, cos A : cos B : cos C = -17 : 67 : 87
收錄日期: 2021-04-27 17:44:11
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20120318000051KK00310