=lim cosx · lim (1-√(cos2x))/x^2=1 · lim (1-(cos2x))/[x^2 · (1+√(cos2x))]=lim (1-(cos2x))/[x^2 · lim(1+√(cos2x))]=lim (1-(cos2x))/[2x^2]=lim (1/2)(2x)²/[2x^2]=1