fx=(x+1)ln(x+1)-ax求导的详细过程

复合函数求导啊（uv）′=uv′+u′v
f′=（x+1）′ln(x+1)+(x+1)(ln(x+1))′-a
=ln(x+1)+(x+1)*1/(x+1)-a
=ln(x+1)+1-a