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Cos3xCos2x=1/2(Cos5x+Cosx)

cos2xcos3x =cos3xcos2x =(1/2){cos(3x+2x)+cos(3

积化和差公式

见图

利用 e^(ix)=cosx+isinx; e^(ix)+e^(i2x)+e^(i3x)+……+e*

cosx*cos2x*cos4x = 2 sinx*cosx*cos2x*cos4x / (2sin

cos(3π/11) =cos(π-8π/11) =-cos(8π/11) cos(5π/11)

没时间回答啦

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