lim1-cosx(cos2x)^(1/2)/x^2=lim1-cosx(cos2x)^(1/2)*1+cosx(cos2x)^(1/2)/{x^21+cosx(cos2x)^(1/2)}=lim1-cosx^2cos2x/{x^21+cosx(cos2x)^(1/2)}=lim1-cosx^2(cosx^2-sinx^2)/{x^21+cosx(cos2x)^(1/2)}=limcosx^2+s...