Thanks, I was able to figure it out with the product rule...
I just wrote it in a different way
f'(x) = (1-x) * [(x^2) +1)]^(-3/2) and used the product rule.
I need the second derivative of f(x)= (x+1)/ sqrt[(x^2) +1]
I got f'(x)= (1-x) / [(x^2) +1]^(3/2)
Solution for f''(x)=[(2x^2) - 3x -1] / [(x^2) +1]^(5/2)
I tried the Quotient Rule but I do not get the solution...
Can someone explain how to get to the solution?