如题所述
sin(a+c)+sin(a-c)=sinacosc+sinccosa +(sinacosc-sinccosa)=2sinacosc
所用常用三角函数sin(a+b)=sinacosb+sinbcosa sin(a-b)=sinacosb-sinbcosa
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第1个回答 2016-10-08
sinB=sin(π-(A+C))=sin(A+C)
sin2C=2sinCcosC
sin2C=2sinCcosC