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

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Sec. 9] Volumes of Solids 163'<br />

Solution. We have<br />

Therefore,<br />

(the latter <strong>in</strong>tegral is taken by<br />

K<br />

-a x a<br />

I/, =6 I^a 2 x 9 and y2 = t>+ Va*x 2<br />

Fig 52<br />

the substitution x=asi<br />

The volume of a solid obta<strong>in</strong>ed by the rotation, about the polar axis, of a<br />

sector formed by an arc of the curve r = F((p) and by two radius vectors<br />

ipr-=a, .<br />

a<br />

by<br />

This same formula is conveniently used when seek<strong>in</strong>g the volume obta<strong>in</strong>ed<br />

the rotation, about the polar axis, of some closed curve def<strong>in</strong>ed <strong>in</strong> polar<br />

coord<strong>in</strong>ates.<br />

Example 3. Determ<strong>in</strong>e the volume formed r = as<strong>in</strong>2(p about the polar<br />

Solution.<br />

axis.<br />

by the rotation of the curve<br />

= 2.--n\ rs<strong>in</strong>q>d(p = yJia 8 C s<strong>in</strong> 8<br />

2(p s<strong>in</strong> q> dcp =<br />

.L<br />

2<br />

= Jia ^ 8 f s<strong>in</strong> 4<br />

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