设函数是f(x)定义在R上的增函数且f(x)≠0,对于任意的x1,x2∈R都有f（x1+x2)=f(x1)(x2).

(1)
令x1=x2=x/2
f(x/2+x/2)=f(x/2)^2
f(x)=f(x/2)^2
由f(x/2)≠0
则f(x)>0
(2)
令x1=x x2=0
得f(x+0)=f(x)*f(0)
f(x)(1-f(0))=0
由f(x)≠0
则1-f(0)=0 f(0)=1
令x1=x x2=-x
f(0)=f(x)*f(-x)
f(-x)=1/f(x)
可知
f(x1-x2)=f(x1)*f(-x2)=f(x1)/f(x2)