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

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336 Differential Equations [C/t. 9<br />

and "<br />

Example 2. Solve the equation f 2xy + x*y + ~ J<br />

Solution. Here P = 2*y + rV-f-^ , Q=x*+y*<br />

.<br />

.<br />

, " ! ' hence> ft=<br />

S<strong>in</strong>ce<br />

d#<br />

_<br />

dx<br />

or ^^^ r<br />

cty<br />

it follows that<br />

+ ' r Qx dx jB, dx<br />

1 .<br />

rffi<br />

. .<br />

fdP dQ\ ^<br />

-<br />

-r ^. ----JS dx=dx and In 11 = ^, 11 = ^.<br />

* r<br />

\\ Q.\dy dxj<br />

Mult<strong>ipl</strong>y<strong>in</strong>g the equation by \i = e* t we obta<strong>in</strong><br />

which is an exact differential equation. Integrat<strong>in</strong>g it, we get the general<br />

<strong>in</strong>tegral<br />

F<strong>in</strong>d the general <strong>in</strong>tegrals of the equations:<br />

2802 (x + t/)d^+(^ + 2z/)dy = 0.<br />

1<br />

2803. (V + 1/ + 2x) dx + 2xydy = Q.<br />

3<br />

2804. (jc S^ 8<br />

+ 2) dx (3x'y y 8 = ) d(/ 0.<br />

2805. ^-^=='<br />

2806. .<br />

y y<br />

2807. F<strong>in</strong>d the particular <strong>in</strong>tegral of the equation<br />

which satisfies the <strong>in</strong>itial condition #(0) = 2.<br />

Solve the equations that admit of an <strong>in</strong>tegrat<strong>in</strong>g factor of the<br />

form fi = M*) or M' = H'(y) :<br />

2808. (x + y*)dx2xydy = 0.<br />

2809. y(l 4-xy)dxxdy = Q.<br />

2810.<br />

281 1.<br />

(jc cos t/ y s<strong>in</strong> r/) rfi/ + (x s<strong>in</strong> */ -( // cos y) dx = 0.

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