Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
 îòðèìàíîìó çàãàëüíîìó ðîçâ’ÿçêó ð³âíÿííÿ (11.5.6)<br />
çàì³íèìî ñòàëó c ôóíêö³ºþ c(x), òîáòî y = c(x)x. Äèôåðåíö³þþ÷è<br />
y, çíàõîäèìî:<br />
y′ = c′<br />
( x) x + c( x)<br />
. (11.5.8)<br />
ϳäñòàâëÿºìî äî ð³âíÿííÿ (11.5.5) øóêàíó ôóíêö³þ<br />
y = c(x)x ³ ¿¿ ïîõ³äíó (11.5.8):<br />
2<br />
′ + − = .<br />
c( x) x c( x) c( x)<br />
x<br />
2<br />
x<br />
Çâ³äñè c′ ( x) = x,<br />
³ cx ( ) = + c0,<br />
äå c<br />
2<br />
0 — äîâ³ëüíà ñòàëà.<br />
ϳäñòàâëÿþ÷è c(x) äî (11.5.7), îñòàòî÷íî çíàõîäèìî çàãàëüíèé<br />
ðîçâ’ÿçîê ð³âíÿííÿ:<br />
3<br />
x<br />
yx ( ) = + cx<br />
0 .<br />
2<br />
Ïðèêëàä 11.5.2. Ðîçâ’ÿçàòè ð³âíÿííÿ<br />
y′ − ytg<br />
x = ctg x. (11.5.9)<br />
Ðîçâ’ÿçàííÿ. Áóäåìî ðîçâ’ÿçóâàòè éîãî ìåòîäîì âàð³àö³¿<br />
äîâ³ëüíî¿ ñòàëî¿. Äëÿ öüîãî ðîçâ’ÿæåìî ñïî÷àòêó ë³í³éíå<br />
îäíîð³äíå ð³âíÿííÿ, â³äïîâ³äíå äî äàíîãî íåîäíîð³äíîãî<br />
y′ − ytg x = 0 .<br />
Öå ð³âíÿííÿ ç â³äîêðåìëþâàíèìè çì³ííèìè, òîìó ëåãêî<br />
ðîçâ’ÿçóºòüñÿ:<br />
dy<br />
dy<br />
= ytg x; = tg xdx;<br />
dx<br />
y<br />
dy<br />
∫ tg xdx; ln y ln cos x ln c<br />
y = ∫ = − + .<br />
²ç îñòàííüî¿ ð³âíîñò³ îòðèìàºìî:<br />
c<br />
y = .<br />
cos x<br />
Ó çíàéäåíîìó çàãàëüíîìó ðîçâ’ÿçêó ë³í³éíîãî îäíîð³äíîãî<br />
ð³âíÿííÿ âàð³þºìî äîâ³ëüíó ñòàëó c, òîáòî øóêàºìî ðîçâ’ÿçîê<br />
ð³âíÿííÿ (11.5.9) ó âèãëÿä³<br />
cx ( )<br />
y = .<br />
cos x<br />
(11.5.10)<br />
ϳäñòàâëÿþ÷è (11.5.10) äî íåîäíîð³äíîãî ð³âíÿííÿ<br />
(11.5.9), ìàºìî<br />
çâ³äêè<br />
c′<br />
( x) sinx tgx<br />
+ cx ( ) − cx ( ) = ctgx<br />
2<br />
,<br />
cos x cos x cos x<br />
2<br />
cos x<br />
c′ ( x) = , à<br />
sin x<br />
cos x 1 − sin x x<br />
cx ( ) = dx= dx= cosx+ ln tg + c<br />
sin x sin x<br />
2<br />
2 2<br />
∫ ∫ 0 .<br />
ϳäñòàâëÿþ÷è çíàéäåíå c(x) â (11.5.10), îäåðæóºìî çàãàëüíèé<br />
ðîçâ’ÿçîê âèõ³äíîãî ð³âíÿííÿ:<br />
x<br />
ln tg 2 c0<br />
y = 1 + cos x<br />
+ .<br />
cos x<br />
Ïðèêëàä 11.5.3. Çíàéòè çàãàëüíèé ðîçâ’ÿçîê ð³âíÿííÿ<br />
2<br />
′ + = . (11.5.11)<br />
y 2xy e −x<br />
Ðîçâ’ÿçàííÿ. Øóêàòè ðîçâ’ÿçîê áóäåìî çà îïèñàíîþ<br />
ñõåìîþ. Ðîçãëÿäàºìî â³äïîâ³äíå îäíîð³äíå ð³âíÿííÿ<br />
y′ + 2xy<br />
= 0.<br />
⎛dy<br />
⎞<br />
³äîêðåìëþþ÷è çì³íí³ ⎜ =−2xdx⎟<br />
³ ³íòåãðóþ÷è, îòðèìàºìî:<br />
⎝ y ⎠<br />
2<br />
2<br />
− x + ln c = ln y ; y = ce −x .<br />
422 423