Integration by Parts
Integration by parts is an important technique in the integration toolbox. It is based on the product rule for differentiation and can be expressed as:
∫ u dv = uv - ∫ v du
Here's how it's typically applied:
- Identify the parts of the integrand: choose which part to differentiate and which to integrate (usually u and dv respectively).
- Differentiate u to find du and integrate dv to find v.
- Plug into the integration by parts formula.
Example
Let's consider the integral ∫ x ex dx:
- Choose u = x → du = dx, dv = ex dx → v = ex
- Apply the formula: ∫ x ex dx = x ex - ∫ ex dx
- Simplify: = x ex - ex + C
This technique is particularly useful for integrals of the form ∫ xn eax dx, ∫ xn sin(ax) dx, and ∫ xn cos(ax) dx.
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