定义域为x>0f(x)=lnx-a(x+1-2)/(x+1)=lnx-a+2a/(x+1)f'(x)=1/x-2a/(x+1)^2>0即[(x+1)^2-2ax]/[x(x+1)^2]>0所以(x+1)^2-2ax>0x^2+(2-2a)x+1>0△=(2-2a)^2-4<0a^2-2a<0a(a-2)<00
