(2006•雙柏縣)閱讀下列材料,并解決后面的問題.
在銳角△ABC中,∠A、∠B、∠C的對邊分別是a、b、c.過A作AD⊥BC于D(如圖),則sinB=
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,sinC=
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,即AD=csinB,AD=bsinC,于是csinB=bsinC,
即
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.同理有
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,
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.
所以
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…(*)
即:在一個三角形中,各邊和它所對角的正弦的比相等.
(1)在銳角三角形中,若已知三個元素a、b、∠A,運用上述結(jié)論(*)和有關(guān)定理就可以求出其余三個未知元素c、∠B、∠C,請你按照下列步驟填空,完成求解過程:
第一步:由條件a、b、∠A
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______
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∠B;
第二步:由條件∠A、∠B
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______
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∠C;
第三步:由條件______
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______
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c.
(2)如圖,已知:∠A=60°,∠C=75°,a=6,運用上述結(jié)論(*)試求b.
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