Юлия lim(e^(4*x)-e^(2*x))^2/(cos(4*x)-cos(x)) = lim(e^(4x)*(e^(2x) - 1)^2/(-2*sin(3/2*x)*sin(5/2*x)) = -lim(4x^2/(15/2*x^2)) = -4/(15/2) = -8/15.