Integration - Transformations

Transformations

Integration by Substitution Techniques

These transformations help simplify complex integrals by changing variables. Substitution is a powerful method for evaluating integrals involving algebraic, trigonometric, exponential, or logarithmic expressions.

  • \[ \int F(ax + b) \, dx = \frac{1}{a} \int F(u) \, du, \quad u = ax + b \]
  • \[ \int F(\sqrt{ax + b}) \, dx = \frac{2}{a} \int u F(u) \, du, \quad u = \sqrt{ax + b} \]
  • \[ \int F(\sqrt[n]{ax + b}) \, dx = \frac{n}{a} \int u^{n-1} F(u) \, du, \quad u = \sqrt[n]{ax + b} \]
  • \[ \int F(\sqrt{a^2 - x^2}) \, dx = a \int F(a \cos u) \cos u \, du, \quad x = a \sin u \]
  • \[ \int F(\sqrt{a^2 + x^2}) \, dx = a \int F(a \sec u) \sec^2 u \, du, \quad x = a \tan u \]
  • \[ \int F(\sqrt{x^2 - a^2}) \, dx = a \int F(a \tan u) \sec u \tan u \, du, \quad x = a \sec u \]
  • \[ \int F(e^{ax}) \, dx = \frac{1}{a} \int \frac{F(u)}{u} \, du, \quad u = e^{ax} \]
  • \[ \int F(\ln x) \, dx = \int F(u) e^u \, du, \quad u = \ln x \]

Terminology

  • Substitution: A method to simplify integration by changing variables.
  • Radical Transform: Used when integrand involves square roots or higher roots.
  • Trigonometric Substitution: Replacing expressions like \( \sqrt{a^2 - x^2} \) with trigonometric identities to ease integration.
  • Exponential & Log Substitution: Applied when integrand involves \( e^{ax} \) or \( \ln x \).

Applications

  • Solving integrals in calculus where direct integration is not possible.
  • Used in physics for changing coordinate systems (e.g., polar to Cartesian).
  • Modeling exponential growth or decay in biology, chemistry, and economics.
  • Solving engineering problems involving trigonometric curves or transformations.
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