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area under the curve bounded by f(x) and x, between the limits x 1 and x 2 : (B.36) Integrals of the type defined by Equation B.36 are called definite integrals. One common integral that arises in practical situations has the form (B.37) This result is obvious, being that differentiation of the right-hand side with respect to x n directly. If the limits of the integration are known, this integral becomes a definite integral and is written (B.38) Examples 1. 2. 3. Partial Integration Sometimes it is useful to apply the method of partial integration (also called “integrating (B.39) where u and v are carefully chosen so as to reduce a complex integral to a simpler one. This can be evaluated by integrating by parts twice. First, if we choose u # x 2 , v # e x , we obtain Now, in the second term, choose u # x, v # e x , which gives '
x
2 e
x
dx # '
x
2
d(e
x ) # x
2 e
x " 2 '
e
x x
dx $ c 1 I(x) # '
x
2 e
x
dx '
u
dv # uv " '
v
du ' 5 3
x
dx # x
2 2 ) 5 3 # 5 2 " 3 2 2 # 8 ' b 0
x
3/2
dx # x
5/2 5/2 ) b 0 # 2 5 b
5/2 ' a 0
x
2
dx # x
3 3 ) a 0 # a
3 3 ' x
2 x 1
x n dx # x
n$1 n $ 1 & x
2 x 1 # x 2 n$1 " x 1 n$1 n $ 1
(n 4 "1) '
x
n dx # x n$1 n $ 1 $ c
(n 4 "1) Area # lim ) x : 0
* i
f
(x i ) )x i # ' x
2 x 1
f
(x) dx A.26 Appendix B • Mathematics Review ∆x i x 2 f(x i ) f(x) x 1 Figure B.14 |