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

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Sec. 10]_Change of Variables_213<br />

or, f<strong>in</strong>ally,<br />

Example 3. Transform the equation<br />

by pass<strong>in</strong>g to the polar coord<strong>in</strong>ates<br />

whence<br />

dx ~xy'<br />

,v=rcoscp, f/ = rs<strong>in</strong>q>. (1)<br />

Solution. Consider<strong>in</strong>g r as a function of cp, from formula (1) we have<br />

dx = cos cp dr r s<strong>in</strong> cp dcp, d// = s<strong>in</strong> cp dr + r cos cp dcp,<br />

dr ,<br />

-<br />

. . . .<br />

, s<strong>in</strong> cp<br />

\ r cos (p<br />

d//_sm cp dr r<br />

-f r cos cp dcp __ dcp<br />

~~<br />

3J cos cp T dr r s<strong>in</strong> cp T d(pr<br />

dr<br />

cos --- cp r s<strong>in</strong> q)<br />

Putt<strong>in</strong>g <strong>in</strong>to the given equation the expressions for x, //, and -^ , we will have<br />

or, after simplifications,<br />

s<strong>in</strong> cp 3- -f r cos cp ^<br />

d

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