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本文介绍对三角命题进行等价转化的一些常用策略 ,供读者参考 .一、和与积的相互转化例 1 求ｓｉｎ7° +ｃｏｓ1 5°ｓｉｎ8°ｃｏｓ7°-ｓｉｎ1 5°ｓｉｎ8°的值 .解 :原式 =ｓｉｎ7° +12 (ｓｉｎ2 3° -ｓｉｎ7°)ｃｏｓ7° +12 (ｃｏｓ2 3° -ｃｏｓ7°)=ｓｉｎ2 3°+ｓ
This article introduces some common strategies for the equivalent transformation of triangular propositions for readers’ reference. First, the inter-transformation of sum and product example 1 Find the value of sin7°+cos1 5°sin8°cos7°-sin1 5°sin8°. Solution: Original =sin7° +12 (sin2 3° -sin7°)cos7° +12 (cos2 3° -cos7°)=sin2 3°+s