Logarithmic Differentiation

Logarithmic Differentiation:

  • Logarithmic differentiation is a technique used to find derivatives of functions that are products, quotients, or powers, especially when the functions are complex or involve variables in both the base and exponent positions.

Steps to Perform Logarithmic Differentiation:

  1. Take the natural logarithm (ln) of both sides of the function you want to differentiate.

  2. Use logarithm properties to simplify the expression:

    • Apply properties such as ln(ab)=ln(a)+ln(b) or ln(an)=nln(a).
  3. Differentiate implicitly with respect to the variable using the chain rule when necessary.

  4. Solve for the derivative in terms of the original function.


Given the function y=xx:

  1. Take the natural logarithm of both sides: ln(y)=ln(xx)

  2. Apply logarithm properties: ln(y)=xln(x)

  3. Differentiate implicitly: 1ydydx=ddx(xln(x)) Using product rule: ddx(xln(x))=1ln(x)+x1x=ln(x)+1

  4. Solve for the derivative: dydx=y(ln(x)+1) Substituting back y=xx : dydx=xx(ln(x)+1)

Tips for Logarithmic Differentiation:

  • Complex Functions:

    • It's particularly useful for functions that involve products, quotients, or powers where direct differentiation becomes cumbersome.
  • Logarithmic Properties:

    • Familiarize yourself with logarithm properties to simplify expressions before differentiation.
  • Handling Multiple Functions:

    • Logarithmic differentiation works well when dealing with multiple functions multiplied, divided, or raised to powers.

Special Cases:

  • Exponential Functions:

    • Logarithmic differentiation is often beneficial for functions involving exponential terms like ax where a is a constant.
  • Trigonometric Functions:

    • It can be used to simplify derivatives involving trigonometric functions when they are raised to variable powers or involve complex combinations.

Advantages of Logarithmic Differentiation:

  • Simplicity in Differentiation:

    • It can simplify the differentiation process for complex functions by using logarithm rules.
  • Handling Indeterminate Forms:

    • Useful in resolving indeterminate forms like 0 or when dealing with limits.