设x1 x2∈(0,正无穷大)且x1<x2∴f(x1)-f(x2)=x1-x2+k x1-k x2=x1-x2+(x2-x1)*k (x1*x2)=(x1-x2)*(1-k (x1*x2))x1-x2<0,当x1*