1、求极限lim(1/x - cotx) ,x趋近于0

(1)lim(x->0) (1/x -cotx)=lim(x->0) (1/x -1/tanx)=lim(x->0) (tanx-x)/(xtanx) (0/0)=lim(x->0) ( (secx)^2 -1 )/ ( x(secx)^2 + tanx )=lim(x->0) (tanx)^2/ ( x(secx)^2 + tanx )=lim(x->0) x / ( (secx)^2 + 1 ...f'(x) <0 这步怎么看出