If f(x)=ln(x+x2+1)f(x) = \ln(x + \sqrt{x^2+1})f(x)=ln(x+x2+1), find f′(x)f'(x)f′(x).
1x2+1\frac{1}{\sqrt{x^2+1}}x2+11
xx2+1\frac{x}{x^2+1}x2+1x
1x+x2+1\frac{1}{x+\sqrt{x^2+1}}x+x2+11
1x2+1\frac{1}{x^2+1}x2+11