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Problems in Mathematical Analysis.pdf - pwp.net.ipl.pt

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Sec. 3\_Integration by Parts_H7<br />

Example<br />

1. F<strong>in</strong>d<br />

Putt<strong>in</strong>g u In*, dv xdx we %<br />

\ x In xdx.<br />

dx x*<br />

have da , v ~~9<br />

2 dx x *<br />

Whence<br />

Sometimes, to reduce a given <strong>in</strong>tegral to tabular form, one has to apply the<br />

fcrmula of <strong>in</strong>tegration by parts several times. In certa<strong>in</strong> cases, <strong>in</strong>tegration<br />

by parts yields an equation from which the desired <strong>in</strong>tegral is determ<strong>in</strong>ed.<br />

Example 2. F<strong>in</strong>d<br />

We have<br />

\ e* cos x dx.<br />

V e* cos x dx = \ e x d (s<strong>in</strong> x) e* s<strong>in</strong> x \ e x s<strong>in</strong> AT dx e x s<strong>in</strong> x +<br />

Hence,<br />

whence<br />

+ \ ex d (cos x) e* s<strong>in</strong> x -\- e x cos x \ e* cos x dx.<br />

\ e* cos x dx e x sm .v-j-e^cos x V e x cos x dx,<br />

cos v dx -- ~ (s<strong>in</strong> x -f- cos .v) -f C.<br />

Apply<strong>in</strong>g the formula of <strong>in</strong>tegration by parts, f<strong>in</strong>d the follow<strong>in</strong>g<br />

<strong>in</strong>tegrals:<br />

1211. ^ \nxdx. 1221. { x s<strong>in</strong> x cos x d\<br />

1212. Jarclanjcdx.<br />

a<br />

1222* (jt +5x+6)cos<br />

$<br />

1213. Jarcs<strong>in</strong> A-rfjc. 1223. ^ x* \nxdx.<br />

1214. Jjcsiiucr/.v.<br />

1215. Jjccos3A'Jx.<br />

1224. Jln'xd*.<br />

1225. (^djc.<br />

1216. Urfjc. 1226. f^d*.<br />

J<br />

J K A<br />

1217. Jx-2-*rfx. 1227. Jjcarctanjcdjc.<br />

1218**. JjV'd*. 1228. Jjcarcsmxdjc.<br />

1219*. (x 2<br />

^2A' + 5)^*dA:. 1229. \n (x + V T~x*) dx.<br />

1220*. '- 1230 '

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