由洛必达法则,lim(x趋近于0) f(1-cosx)/tan(x2)=lim(x趋近于0) f'(1-cosx)*sinx/[-2x/cos(x^2)] =[lim(x趋近于0)-cos(x^2)* f'(1-cosx)]*[[lim(x趋近于0)sinx/x]=-f"(0)/2=0.
