=lim (1-2sin^√x/2)*1/x
=lim (1-x/2)*1/x
令x=1/n,n-->∞
原式=lim (1-1/2n)^n
=lim (1-1/2n)^[2n*1/2]
=1/e^[1/2]
=e^[-1/2]