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(cCosA,cSinA)

y. y. y. B. (bCosC,bSinC). C. A. c. a. a. c. b. b. c. a. A C. o x. B A. C B. o x. o x. S △ = bcSinA. S △ = caSinB. S △ = abSinC. 三角形的面积等于任意两边与 它们夹角的正弦的积的一半。. 结论. (cCosA,cSinA). (aCosB,aSinB). b. bcSinA= caSinB= abSinC.

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(cCosA,cSinA)

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  1. y y y B (bCosC,bSinC) C A c a a c b b c a A C o x BA CB ox ox S△= bcSinA S△=caSinB S△=abSinC 三角形的面积等于任意两边与 它们夹角的正弦的积的一半。 结论 (cCosA,cSinA) (aCosB,aSinB) b

  2. bcSinA= caSinB= abSinC A c b 即== C B a bSinA= aSinB 在一个三角形中，各边和它 所对的角的正弦的比相等。 正弦定理：

  3. 1 在 中，已知 ，求 . 解：由 得 所以A= ∵ 在 中 另一判断方法： ∴ A ＜Ｂ，即Ａ为３０度．

  4. B 10 2 在 中，已知 ，求b（保 留两个有效数字）. A b C 解：∵

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