(x→0）lim{(1-cosx)/x³}= (x→0）lim{[1-1+2sin²(x/2)]/x³}= (x→0）lim{2sin²(x/2)]/8*(x/2)³}= (x→0）lim{sin²(x/2)]/4*(x/2)³}= (x→0）lim{(x/2)²]/4*(x/2)³}= +∞
洛必达法则呀
