(2)lim(1-cosx)/x^2=lim(2(sin(x/2))^2)/x^2=lim(2(sin(x/2))^2)/x^2
=lim(2*(x/2)^2)/x^2=1/2(等价无穷小 sin x/2=x/2)
(5)洛毕塔法则
=lim（e^x-cosx*e^x）/(1-cosx)
=lim（e^x-cosx*e^x+sinx*e^x）/(sin x)
=lim（e^x-cosx*e^x+2sinx*e^x+cosx*e^x）/(cosx)
=lim（e^x+2sinx*e^x）/(cosx) (代入x=0)
=1