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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 uu and which should be dvdv 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 udv=uvvdu\int u\,dv = uv - \int v\,du. LIATE suggests choosing uu in this order: logarithmic, inverse trigonometric, algebraic, trigonometric, exponential. Repeated parts is useful when each step makes uu simpler, such as in x2exdx\int x^2 e^x\,dx.

The tabular method is a shortcut for repeated parts when derivatives eventually reach 00 or form a simple pattern.

Key Facts

  • The integration by parts formula is udv=uvvdu\int u\,dv = uv - \int v\,du.
  • The definite integral form is abudv=[uv]ababvdu\int_a^b u\,dv = \left[uv\right]_a^b - \int_a^b v\,du.
  • LIATE ranks choices for uu as logarithmic, inverse trigonometric, algebraic, trigonometric, then exponential.
  • After choosing uu, compute dudu by differentiating and compute vv by integrating dvdv.
  • Choose uu so that dudu is simpler than uu, such as choosing u=x3u = x^3 because du=3x2dxdu = 3x^2\,dx.
  • For xexdx\int x e^x\,dx, choose u=xu = x and dv=exdxdv = e^x\,dx to get xexdx=xexex+C\int x e^x\,dx = x e^x - e^x + C.
  • For lnxdx\int \ln x\,dx, use u=lnxu = \ln x and dv=dxdv = dx to get lnxdx=xlnxx+C\int \ln x\,dx = x\ln x - x + C.
  • 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 udv\int u\,dv as uvvduuv - \int v\,du.
LIATE
A guideline for choosing uu 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 dudu or dvdv that represents the derivative part used to track substitution and integration steps.
Antiderivative
A function F(x)F(x) whose derivative is the original function, so F(x)=f(x)F'(x) = f(x).

Common Mistakes to Avoid

  • Choosing uu only because it appears first is wrong because the best uu should usually become simpler when differentiated.
  • Forgetting to integrate dvdv is wrong because the formula requires vv, not just dvdv, in the product uvuv.
  • Dropping the minus sign in uvvduuv - \int v\,du 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 CC in an indefinite integral is wrong because all antiderivatives differ by a constant.

Practice Questions

  1. 1 Use integration by parts to evaluate xcosxdx\int x\cos x\,dx.
  2. 2 Use LIATE to evaluate x2exdx\int x^2 e^x\,dx.
  3. 3 Evaluate the definite integral 01xe2xdx\int_0^1 x e^{2x}\,dx.
  4. 4 Explain why LIATE usually suggests choosing u=lnxu = \ln x instead of u=xu = x in xlnxdx\int x\ln x\,dx.