(本小題滿分8分)
在
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中,
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,

,

.
(Ⅰ)求

的值;
(Ⅱ)求

的值.
(Ⅰ)

(Ⅱ)

解:(Ⅰ)因為
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,根據(jù)正弦定理知,
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,即

;
(Ⅱ)利用余弦定理的推論得

,易得

,
因此
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,

,
所以
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.
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