令t=1/x,t趋于0
lim(sint+cost)^(1/t)
=lim[1+(sint+cost-1)]^{[1/(sint+cost-1)]*(sint+cost-1)/t}
再因为t趋于0时,lim(sint+cost-1)/t=lim(cost-sint)=1
所以
lim(sint+cost)^(1/t)
=lim[1+(sint+cost-1)]^{[1/(sint+cost-1)]*(sint+cost-1)/t}
=e