在
ABC中,
a,
b,
c分別是三個內(nèi)角
A,
B,
C的對邊,設(shè)

.
(Ⅰ)求

的值;
(Ⅱ)求
ABC的面積.
解:(Ⅰ)由余弦定理,得

. ------------5分
(Ⅱ)因為

,

,所以

,-------7分
所以
ABC的面積

. --------------10分
本試題主要是考查了解三角形中余弦定理的求解和三角形面積公式的綜合運用。
(1)由余弦定理,得

(2)因為

,

,所以

,結(jié)合正弦面積公式得到。
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