Integration by Parts: Learn It 2

How to Choose [latex]u[/latex] and[latex]dv[/latex]

The natural question you’re probably asking is: How do I know which part should be [latex]u[/latex] and which should be [latex]dv[/latex]? Sometimes it takes some trial and error, but there’s a helpful strategy that can guide your choices.

The LIATE Method

The acronym LIATE can help take the guesswork out of choosing [latex]u[/latex] and [latex]dv[/latex]:

  • Logarithmic Functions
  • Inverse Trigonometric Functions
  • Algebraic Functions
  • Trigonometric Functions
  • Exponential Functions

Rule: Choose [latex]u[/latex] to be the function type that appears first in this list.

For example, if your integral contains both a logarithmic function and an algebraic function, choose [latex]u[/latex] to be the logarithmic function since L comes before A in LIATE.

Why Does LIATE Work?

This mnemonic works because of integration practicality:

  • Logarithmic and inverse trig functions are at the front because we don’t have simple integration formulas for them—so they make poor choices for [latex]dv[/latex]
  • Exponential and trig functions are at the end because they’re easy to integrate and make excellent choices for [latex]dv[/latex]
  • Algebraic functions are in the middle because they’re generally manageable both to integrate and differentiate
To use the by-parts technique successfully, it is helpful to first review the derivative rules of several familiar transcendental functions.

  1. [latex]\frac{d}{dx} (\sin x) = \cos x[/latex]
  2. [latex]\frac{d}{dx} (\cos x) = -\sin x[/latex]
  3. [latex]\frac{d}{dx} (\ln x) = \frac{1}{x}[/latex]
  4. [latex]\frac{d}{dx} (\arcsin x) = \frac{1}{\sqrt{1-x^2}}[/latex]
  5. [latex]\frac{d}{dx} (\arctan x) = \frac{1}{1+x^2}[/latex]

Now let’s see how this method works in practice.

Evaluate [latex]\displaystyle\int \frac{\text{ln}x}{{x}^{3}}dx[/latex].

In some cases it may be necessary to apply integration by parts more than once.

Evaluate [latex]{\displaystyle\int }^{\text{ }}{x}^{2}{e}^{3x}dx[/latex].

Evaluate [latex]{\displaystyle\int }^{\text{ }}\sin\left(\text{ln}x\right)dx[/latex].

CautionCaution! LIATE is a guide, not a rigid rule. If your first choice leads to an integral you can’t evaluate, try a different approach.

Evaluate [latex]{\displaystyle\int }^{\text{ }}{t}^{3}{e}^{{t}^{2}}dt[/latex].