可以使用积化和差公式求解.刚才解答有误,抱歉.sin20°sin40°sin80° =-(1/2)[cos60°-cos(-20°)]sin80° =-(1/4)sin80°+(1/2)cos20°*sin80° =-(1/4)sin80°+(1/2)*(1/2)(sin100°+sin60°) =-(1/4)sin80°+(1/4...