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²íòåãðóþ÷è,<br />
ìàºìî<br />
ln x ln c ln 1 z<br />
2<br />
=<br />
1<br />
− − , çâ³äê³ëÿ<br />
2<br />
2<br />
x 1 − z = c1<br />
, àáî x(1 − z ) = ± c . Ïîêëàäåìî ±c<br />
1<br />
1 = c, òîä³<br />
2<br />
c = x(1 − z ) , àáî îñòàòî÷íî<br />
2<br />
⎛<br />
c x 1 y ⎞<br />
= ⎜ −<br />
2 ⎟<br />
⎝ x ⎠ .<br />
Ïðèêëàä 11.4.6. Ïðî³íòåãðóâàòè ð³âíÿííÿ<br />
dy xy<br />
=<br />
2 2<br />
dx<br />
. (11.4.21)<br />
x − y<br />
Ðîçâ’ÿçàííÿ. ijëÿ÷è ÷èñåëüíèê ³ çíàìåííèê ïðàâî¿<br />
÷àñòèíè ð³âíÿííÿ (11.4.21) íà x 2 , îòðèìàºìî<br />
dy y / x<br />
=<br />
dx 1 − y/<br />
x<br />
( ) 2<br />
Ðîáèìî çàì³íó y z<br />
x = , òîä³ dz z<br />
z + x = dx<br />
2 .<br />
1 − z<br />
³äîêðåìëþþ÷è çì³íí³, áóäåìî ìàòè<br />
z<br />
²íòåãðóþ÷è, çíàõîäèìî:<br />
1<br />
2z<br />
ln ln ln<br />
2<br />
1 − z dx<br />
dz<br />
3<br />
= .<br />
x<br />
− − z = x + c<br />
2<br />
àáî 2<br />
.<br />
1<br />
− = ln zxc .<br />
2z<br />
y<br />
ϳäñòàâëÿþ÷è â îñòàííþ ð³âí³ñòü z = , îòðèìàºìî çàãàëüíèé<br />
³íòåãðàë âèõ³äíîãî<br />
x<br />
ð³âíÿííÿ:<br />
2<br />
x<br />
− = ln cy<br />
2 .<br />
2y<br />
Çàóâàæåííÿ. гâíÿííÿ âèãëÿäó<br />
Mxydx ( , ) + Nxydy ( , ) = 0<br />
áóäå îäíîð³äíèì ó òîìó ³ ò³ëüêè ó òîìó âèïàäêó, ÿêùî<br />
ôóíêö³¿ M(x, y) ³ N(x, y) º îäíîð³äíèìè ôóíêö³ÿìè îäíîãî é<br />
òîãî ñàìîãî ñòåïåíÿ, òîáòî ÿêùî M(λx, λy) =λ n M(x, y) ³<br />
N(λx, λy)=λ n N(x, y), äå λ > 0 — äîâ³ëüíå ÷èñëî, n — ñòåï³íü<br />
îäíîð³äíîñò³.<br />
Ïðèêëàä 11.4.11. Ðîçâ’ÿçàòè ð³âíÿííÿ<br />
( )<br />
+ − = 0 . (11.4.22)<br />
2 2<br />
y xy dx x dy<br />
2<br />
Öå ð³âíÿííÿ º îäíîð³äíèì, îñê³ëüêè ôóíêö³¿ y + xy ³<br />
x 2 — îäíîð³äí³ ôóíêö³¿ äðóãîãî ñòåïåíÿ.<br />
Ðîçâ’ÿçàííÿ. ijëèìî îáèäâ³ ÷àñòèíè ð³âíÿííÿ<br />
(11.4.22) íà x 2 ³ ðîçâ’ÿçóºìî â³äíîñíî ïîõ³äíî¿. Îòðèìàºìî:<br />
Ââîäÿ÷è íîâó ôóíêö³þ<br />
Ðîçâ’ÿçóþ÷è éîãî<br />
2<br />
dy ⎛⎛y ⎞ y ⎞<br />
= +<br />
dx ⎜⎜<br />
x<br />
⎟<br />
⎝ ⎠ x ⎟<br />
⎝ ⎠ .<br />
y<br />
z = , áóäåìî ìàòè ð³âíÿííÿ<br />
x<br />
2 dz<br />
z + z = z + x . dx<br />
= dz dz dx 1<br />
, , ln<br />
dx z<br />
= x − z<br />
= +<br />
2<br />
z x x c<br />
2<br />
³ ïîâåðòàþ÷èñü äî ñòàðèõ çì³ííèõ, îòðèìàºìî çàãàëüíèé<br />
ðîçâ’ÿçîê<br />
x<br />
x<br />
− = ln x + c ⇒ y = −<br />
y c + ln x<br />
.<br />
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