text: # How do you find int (2x)/(x^2+1)dx?
  
  Feb 4, 2015
  
  The answer is: $\ln \left({x}^{2} + 1\right) + c$.
  
  Since the numerator is the derivative of the denominator, using this rule:
  
  $\int \frac{f ' \left(x\right)}{f} \left(x\right) \mathrm{dx} = \ln f \left(x\right) + c$