Ответ Автор - армения20171 cos5π/7+cos3π/4 ??cos(π-2π/7)+cos(π-π/4)=-cos(2π/7)-cos(π/4)=-(cos2π/7+cosπ/4)<0(cos(2π/7)>0;cos(π/4)>0)(cos5π/7+cos3π/4)<0