令a=x²则a≥0y=(1-a)/(1+a)=-(a-1)/(a+1)=-(a+1-2)/(a+1)=-[(a+1)/(a+1)-2/(a+1)]=-1+2/(a+1)a+1≥10<1/(a+1)≤10<2/(a+1)≤2减去1-1<2/(a+1)-1≤1所以值域(-1,1]
(1-x)/(1+x)
