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单词 IntegrationByParts
释义

integration by parts


When we want to integrate a product of two functions, it is sometimes preferable to simplify the integrand by integrating one of the functions and differentiating the other. This process is called integrating by parts, and is done in the following way, where u and v are functions of x.

uv𝑑x=uv-vu𝑑x

This process may be repeated indefinitely, and in some cases it may be used to solve for the original integral algebraically. For definite integrals, the rule appears as

abu(x)v(x)𝑑x=(u(b)v(b)-u(a)v(a))-abv(x)u(x)𝑑x

Proof:Integration by parts is simply the antiderivative of a product ruleMathworldPlanetmath. Let G(x)=u(x)v(x). Then,

G(x)=u(x)v(x)+u(x)v(x)

Therefore,

G(x)-v(x)u(x)=u(x)v(x)

We can now integrate both sides with respect to x to get

G(x)-v(x)u(x)𝑑x=u(x)v(x)𝑑x

which is just integration by parts rearranged.
Example: We integrate the function f(x)=xsinx: Therefore we define u(x):=x and v(x)=sinx. So integration by parts yields us:

xsinx𝑑𝑥=-xcosx+cosx𝑑𝑥=-xcosx+sinx+C,

where C is an arbitrary constant.

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更新时间:2025/5/4 18:59:06