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

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Sec. 5] Bernoulli's Equation 333<br />

Consider<strong>in</strong>g C as a function of x, and differentiat<strong>in</strong>g, we fi'nd;<br />

cos x<br />

dC s<strong>in</strong> x ~ A I /,x>o2 2<br />

dx cos x<br />

~<br />

'<br />

Putt<strong>in</strong>g y and y' <strong>in</strong>to (4), we get:<br />

whence<br />

1 dC .<br />

s<strong>in</strong>*<br />

C ,<br />

cos* djc cos 2 * cos*<br />

= Ccos 2 *d*==i-* + j<br />

dC<br />

'<br />

dx<br />

, or -r-=<br />

Hence, the general solution of equation (4) has the form<br />

COS*<br />

In solv<strong>in</strong>g the l<strong>in</strong>ear equation (1) we can also make use of the substitution<br />

y uv t (5)<br />

where u and v are functions of x. Then equation (1) will have the form<br />

If we require that<br />

f<br />

[u<br />

\-P(x)u]v + v'u^Q(x). (6)<br />

'<br />

+ P(jc)M = 0, (7)<br />

then from (7) we f<strong>in</strong>d M, and from (6) we f<strong>in</strong>d u; hence, from (5) we f<strong>in</strong>d y.<br />

2\ Bernoulli's equation. A first order equation of the form<br />

y' + P (

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