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

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Sec. 8] Improper Integrals Dependent on a Parameter 260<br />

distance of the<br />

of the solid.<br />

po<strong>in</strong>t from the centre. F<strong>in</strong>d the centre of gravity<br />

2268. F<strong>in</strong>d the centre of gravity of a solid bounded by the<br />

2<br />

paraboloid // +2z 2 = 4x and the plane x=2.<br />

2269*. F<strong>in</strong>d the moment of <strong>in</strong>ertia of a circular cyl<strong>in</strong>der,<br />

whose altitude is h and the radius of the base is a, relative to<br />

the axis which serves as the diameter of the<br />

2270*. F<strong>in</strong>d the moment of <strong>in</strong>ertia<br />

base of the cyl<strong>in</strong>der.<br />

of a circular con^<br />

(altitude, /i, radius of base, a, and density Q) relative to<br />

the diameter of the base.<br />

2271**. F<strong>in</strong>d the force of attraction exerted by a homogeneous<br />

cone of altitude h and vertex angle a (<strong>in</strong> axial cross-section) on<br />

a material po<strong>in</strong>t conta<strong>in</strong><strong>in</strong>g unit mas^ and located at its vertex.<br />

2272**. Show that the force of attraction exerted by a homo-<br />

geneous sphere on an external material po<strong>in</strong>t does not change if<br />

the entire mass of the sphere is concentrated at its centre.<br />

Sec. 8. Improper Integrals Dependent on a Parameter.<br />

Improper Mult<strong>ipl</strong>e Integrals<br />

1. Differentiation with respect to a parameter. In the case of certa<strong>in</strong><br />

restrictions imposed on the functions / (.v, a), f'a (x, a) and on the correspond-<br />

<strong>in</strong>g improper <strong>in</strong>tegrals<br />

Then<br />

\vc have the Leibniz rule<br />

(.v, a) dx = \<br />

a 'i<br />

fa (A-, a) dx.<br />

Example 1. By differentiat<strong>in</strong>g with respect to a parameter, evaluate<br />

Solution. Let<br />

\<br />

da<br />

><br />

~~<br />

dx (a > 0, p > 0).<br />

~ 1 2a "2a*<br />

Whence F (a, p) = - Ina + C(p). To f<strong>in</strong>d C(p), we put<br />

equation. We have 0= ~ In P + C(P).<br />

Whence C(p) = -^-lnp. Hence,<br />

a = <strong>in</strong> the latter

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