Sin20°*sin40°*sin60°*sin80°的乘积和完整步骤

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.