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Definite Integration By Parts

Integration by parts requires a great deal of guesswork. Given a problem ∫ h(x) dx we try to find a way to split h(x) dx into a product f(x) g'(x) dx where we can evaluate both of the integrals ∫ g'(x) dx and ∫ g(x) f'(x) dx.

Definite integrals take the following form when integration by parts is applied.

DEFINITE INTEGRATION BY PARTS

If u = f(x) and v = g(x) have continuous derivatives on an open interval I, then for a, b in I,

07_trigonometric_functions-238.gif

PROOF

The Product Rule gives

f(x) g'(x) dx + g(x)f'(x) dx = d(f(x) g(x)).

Then by the Fundamental Theorem of Calculus,

07_trigonometric_functions-239.gif

and the desired result follows by the Sum Rule.

If we plot u = f(x) on one axis and v = g(x) on the other, we get a picture of definite integration by parts (Figure 7.4.1). The picture is easier to interpret if we change variables in the definite integrals and write the formula for integration by

07_trigonometric_functions-240.gif

Figure 7.4.1 Definite Integration by Parts parts in the form

07_trigonometric_functions-241.gif


Last Update: 2006-11-05