设F（X）=x-In(x+1) ,x》0
x>0时,F'(X)=1-1/(x+1)=x/（x+1）,x>0
从而F(X )在[0,正无穷）上单调递增,
故x>0时,F(X)>F(0)=0
即：x>In(x+1)