Understanding Integration by Parts
The Integration by Parts Calculator applies the fundamental formula ∫ u dv = uv − ∫ v du to your pre-evaluated numerical terms. Enter the values of the uv product and the ∫ v du correction integral, and the calculator returns the final result along with a breakdown of each component. This technique is a cornerstone of calculus, essential for solving integrals involving products of functions in physics, engineering, and applied mathematics.
The Integration by Parts Formula
Integration by parts is derived from the product rule of differentiation and transforms a difficult integral into a potentially simpler one. You choose which part of the integrand to differentiate (u) and which to integrate (dv), then apply:
∫ u dv = uv − ∫ v du
The calculator evaluates this as:
Result = Evaluated uv − Evaluated ∫ v du
Evaluated uv is the numerical value of u times v (after substituting bounds for definite integrals or simplifying for indefinite ones), and Evaluated ∫ v du is the numerical value of the remaining integral after performing the integration.
Worked Example: Evaluating ∫ x·e^x dx
A calculus student needs to evaluate an integral using integration by parts. They have chosen u = x and dv = e^x dx, and after working through the symbolic steps, determined that the uv term evaluates to 20 and the ∫ v du term evaluates to 7.5.
- Identify the formula: ∫ u dv = uv − ∫ v du
- Substitute evaluated terms: ∫ u dv = 20 − 7.5
- Calculate: 20 − 7.5 = 12.5
- Interpret: The result is positive (12.5), meaning the uv term (20) dominates the ∫ v du correction (7.5). The uv term is 2.67 times larger than the correction.
The calculator displays three cards: ∫ u dv (Result) = 12.5, uv Term = 20, and ∫ v du Correction = 7.5.
Strategies for Choosing u and dv
The success of integration by parts depends on choosing u and dv wisely. The LIATE mnemonic suggests choosing u from the earliest applicable category:
- Logarithmic functions (e.g., ln x)
- Inverse trigonometric functions (e.g., arctan x)
- Algebraic functions (e.g., x, x^2)
- Trigonometric functions (e.g., sin x, cos x)
- Exponential functions (e.g., e^x, 2^x)
For ∫ x·e^x dx, x (Algebraic) comes before e^x (Exponential), so u = x and dv = e^x dx. Differentiating u gives du = dx (simpler), and integrating dv gives v = e^x (straightforward). The new integral ∫ e^x dx is much simpler than the original.
When Integration by Parts Must Be Applied Repeatedly
Some integrals require multiple applications of integration by parts, or a technique called tabular integration. For example, ∫ x^2·e^x dx requires two rounds: the first reduces x^2 to x, and the second reduces x to 1. Each round produces a new uv term and a new ∫ v du that becomes the next integral. You can use this calculator at each stage, entering the evaluated terms for that round, and save each step using the Recent history to track your work through the full solution.
