f(x)=kx+lnx,当k=0是,是否存在不相等的正数a、b满足[f(a)-f(b)]/(a-b)=f ‘[（a+b)/2]?k=0时,f(x)=lnx,f′(x)=1/x,lna-lnb=ln(a/b)=(a-b)[2/(a+b)]=2(a-b)/(a+b)设a/b=m,a=mb,ln(a/b)=ln(mb/b)=lnm=2(mb-b)/(mb+b)=2...