周期为4mf(x+2m)=f[(x+m)+m]=[1+f(x+m)]/[1-f(x+m)]⑴f（x+m）=[1+f(x)]/[1-f(x)]⑵由⑴⑵推出f(x+2m)=-(1/f(x)) ⑶f(x+4m)=f[(x+2m)+2m]=-(1/f(x+2m))=f(x)所以f(x)为周期函数,周期为4m