Derivatives of Exponential and Logarithmic Functions: Fresh Take

  • Determine the derivatives of exponential and logarithmic functions
  • Apply logarithmic differentiation to find derivatives

Derivative of the Exponential Function

The Main Idea 

  • The Natural Exponential Function:
    • Defined as [latex]E(x) = e^x[/latex]
    • [latex]e \approx 2.718281828...[/latex]
  • Key Property:
    • [latex]\frac{d}{dx}(e^x) = e^x[/latex]
  • General Exponential Function:
    • For [latex]B(x) = b^x[/latex] where [latex]b > 0[/latex]: [latex]B'(x) = b^x B'(0)[/latex]
  • Chain Rule Application:
    • [latex]\frac{d}{dx}(e^{g(x)}) = e^{g(x)} g'(x)[/latex]

Find the derivative of [latex]h(x)=xe^{2x}[/latex].

Find the derivative of [latex]f(x) = e^{\tan(2x)}[/latex].

If [latex]A(t)=1000e^{0.3t}[/latex] describes the mosquito population after [latex]t[/latex] days, as in the preceding example, what is the rate of change of [latex]A(t)[/latex] after 4 days?

Derivative of the Logarithmic Function

The Main Idea 

  • Derivative of Natural Logarithm:
    • For [latex]x > 0[/latex], if [latex]y = \ln x[/latex], then [latex]\frac{dy}{dx} = \frac{1}{x}[/latex]
  • General Logarithmic Derivative:
    • For [latex]h(x) = \ln(g(x))[/latex], [latex]h'(x) = \frac{g'(x)}{g(x)}[/latex]
  • Derivative of General Base Logarithm:
    • For [latex]b > 0, b \neq 1[/latex], if [latex]y = \log_b x[/latex], then [latex]\frac{dy}{dx} = \frac{1}{x \ln b}[/latex]
  • Derivative of General Exponential:
    • For [latex]b > 0, b \neq 1[/latex], if [latex]y = b^x[/latex], then [latex]\frac{dy}{dx} = b^x \ln b[/latex]

Differentiate: [latex]f(x)=\ln (3x+2)^5[/latex].

Find the derivative of [latex]f(x) = \ln(\frac{x^2 \sin x}{2x+1})[/latex].

Find the slope of the tangent line to [latex]y = \log_2(3x+1)[/latex] at [latex]x = 1[/latex].

Find the slope for the line tangent to [latex]y=3^x[/latex] at [latex]x=2[/latex].

Logarithmic Differentiation

The Main Idea 

  • Purpose:
    • Simplify differentiation of complex functions, especially those involving products, quotients, and exponents
  • Applications:
    • Functions of the form [latex]y = (g(x))^n[/latex]
    • Functions like [latex]y = b^{g(x)}[/latex]
    • Expressions such as [latex]y = x^x[/latex] or [latex]y = x^{\pi}[/latex]

Step-by-Step Process

  1. Take natural logarithm of both sides: [latex]\ln y = \ln(h(x))[/latex]
  2. Expand using logarithm properties
  3. Differentiate both sides implicitly
  4. Solve for [latex]\frac{dy}{dx}[/latex]
  5. Simplify the final expression

Key Logarithm Properties

  • Product Rule: [latex]\log_b(MN) = \log_b(M) + \log_b(N)[/latex]
  • Quotient Rule: [latex]\log_b(\frac{M}{N}) = \log_b(M) - \log_b(N)[/latex]
  • Power Rule: [latex]\log_b(M^n) = n\log_b(M)[/latex]
  • Change of Base: [latex]\log_b(M) = \frac{\log_n(M)}{\log_n(b)}[/latex]

Find the derivative of [latex]y=\large \frac{x\sqrt{2x+1}}{e^x \sin^3 x}[/latex]

Use logarithmic differentiation to find the derivative of [latex]y=x^x[/latex].

Find the derivative of [latex]y=(\tan x)^{\pi}[/latex].

Find the derivative of [latex]y = (2x^4 + 1)^{\tan x}[/latex].

Find the derivative of [latex]y = x^r[/latex] where [latex]r[/latex] is any real number.