Integration by parts is a method for finding antiderivatives of products, especially when substitution does not simplify the integral. This cheat sheet helps students choose which factor should be and which should be using the LIATE guideline. It also organizes repeated integration by parts and the tabular method so multi-step problems are easier to manage.
Students need these tools for polynomial, exponential, logarithmic, inverse trig, and trigonometric products.
The main formula comes from the product rule and is written as . LIATE suggests choosing in this order: logarithmic, inverse trigonometric, algebraic, trigonometric, exponential. Repeated parts is useful when each step makes simpler, such as in .
The tabular method is a shortcut for repeated parts when derivatives eventually reach or form a simple pattern.
Key Facts
- The integration by parts formula is .
- The definite integral form is .
- LIATE ranks choices for as logarithmic, inverse trigonometric, algebraic, trigonometric, then exponential.
- After choosing , compute by differentiating and compute by integrating .
- Choose so that is simpler than , such as choosing because .
- For , choose and to get .
- For , use and to get .
- In tabular integration, multiply diagonally with alternating signs , , , until the derivative column ends or repeats.
Vocabulary
- Integration by Parts
- A technique for integrating products that rewrites as .
- LIATE
- A guideline for choosing in integration by parts, ordered as logarithmic, inverse trigonometric, algebraic, trigonometric, and exponential.
- Tabular Method
- A shortcut for repeated integration by parts that organizes derivatives, integrals, and alternating signs in a table.
- Repeated Integration by Parts
- Using integration by parts more than once in the same problem, usually because the remaining integral is still a product.
- Differential
- A notation such as or that represents the derivative part used to track substitution and integration steps.
- Antiderivative
- A function whose derivative is the original function, so .
Common Mistakes to Avoid
- Choosing only because it appears first is wrong because the best should usually become simpler when differentiated.
- Forgetting to integrate is wrong because the formula requires , not just , in the product .
- Dropping the minus sign in is wrong because it changes the value of the antiderivative.
- Using LIATE as an absolute rule is wrong because it is a guideline, and some integrals require a different choice to become simpler.
- Forgetting the constant in an indefinite integral is wrong because all antiderivatives differ by a constant.
Practice Questions
- 1 Use integration by parts to evaluate .
- 2 Use LIATE to evaluate .
- 3 Evaluate the definite integral .
- 4 Explain why LIATE usually suggests choosing instead of in .