f(m+n)=f(m)+f(n)-1
f(0)=f(0)+f(0)-1
f(0)=1
f(0)=f(0.5)+f(-0.5)-1
因为f(0.5)=2所以
f(-0.5)=0
假设x1>x2 都属于R
证明f(x1)-f(x2)>0即可
f(x1)=f(x1-x2)+f(x2)-1
f(x1)-f(x2)=f(x1-x2)-1
x1-x2>0
f(x1-x2)=f(0.5)+f(x1-x2-0.5)-1=1+f(x1-x2-0.5)
因为x1-x2>0
所以x1-x2-0.5>-0.5
所以f(x1-x2-0.5)>0
所以f(x1-x2)=f(0.5)+f(x1-x2-0.5)-1=1+f(x1-x2-0.5)>1
f(x1)-f(x2)=f(x1-x2)-1>0证毕