Integral of Logarithmic Function to Any Base : Log_a (x)

The steps to find the integral of a logarithmic function to any base are presented.

Use of the Change of Base Formula

Let \( y = \log_a x \)
Use the change of base formula to rewrite \( y = \log_a x \) using the natural logarithm \( \ln \) as
\[ y = \log_a x = \dfrac{\ln x}{\ln a} \] We now evaluate the integral \[ \int \log_a x \; dx = \int \left(\dfrac{ \ln x }{\ln a}\right)\; dx \] \( \ln a \) is a constant and therefore \[ \int \log_a x \; dx = \dfrac{ 1}{\ln a} \int \ln x \; dx \qquad (I) \] The integral of ln x is given by \[ \int \ln x \; dx = x \ln x - x + c \] Substitute in \( (I) \) to obtain
\[ \displaystyle \int \log_a x \; dx = \dfrac{ 1}{\ln a} (x \ln x - x) + c \]



More References and Links

  1. change of base formula
  2. Integral of ln x
  3. Chain Rule of Differentiation in Calculus
  4. Convert Logarithms and Exponentials
  5. Rules of Logarithm and Exponential - Questions with Solutions