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
- [latex]\frac{d}{dx} (\sin x) = \cos x[/latex]
- [latex]\frac{d}{dx} (\cos x) = -\sin x[/latex]
- [latex]\frac{d}{dx} (\ln x) = \frac{1}{x}[/latex]
- [latex]\frac{d}{dx} (\arcsin x) = \frac{1}{\sqrt{1-x^2}}[/latex]
- [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].
Caution! 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].