Sin20°*sin40°*sin60°*sin8 - 知识问答

Sin20°*sin40°*sin60°*sin80°的乘积和完整步骤

1个回答

积化和差2sinasinb=cos(a-b)-cos(a+b),2sinacosb=sin(a+b)+sin(a-b).
sin20sin40sin60sin80
=[(cos20-cos60)sin80]sin60/2
=[(sin100+sin60)/2-sin80/2]sin60/2
=(sin60/2)^2
=3/16.

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