Сборник задач по высшей математике 2 том
.pdf2.5.7. |
PernuTb YPaBHeHue: y..,fjj'=l = 2 - |
y'. |
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Pa3pernUM 3a,rr.aHHoe ypaBHeHue OTHOCUTe.JIbHO y, a 3aTeM nOJIO)l{UM y' = |
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= p, Tor.n;a nOJIY'iUM |
2-p |
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(5.4) |
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y= -- . |
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Jp-l
,dy
,naJIee, TaK KaK Y = dx' TO
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dy |
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d (Jp-!l) |
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-y'1J=l-2Jp - 1 d |
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dp |
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2-p |
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dx = - |
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= --'----=----''- |
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p -- |
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y' |
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p |
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(P-l)p |
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2(p-l)! |
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oTKy.n;a, nOCJIe uHTerpupOBaHUjI, nOJIY'iUM |
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1 |
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(5.5) |
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x= .~+C. |
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vp-l |
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HCKJIID'iUBnapaMeTp p U3 ypaBHeHUjI (5.5), HaxO.n;UM |
= x - C, T.e. |
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vP- ~ |
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p = 1+ |
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2'Hait.n;eHHoe Bblpa:>KeHUe .n;JIjI p no.n;CTaBUM B paBeHCTBO (5.4): |
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(x - |
C) |
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2-1- |
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Y = |
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(x - C)2 |
= X _ C __I_ |
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x-c |
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C)2 - |
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- o6rn;ee perneHue UCXO.n;HOro ypaBHeHUjI. |
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PeUJ,umb |
ypa6HeHtJ.H.: |
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2.5.8. |
y = VI - y,2 + y'. |
2.5.9. |
y' = In(xy' - |
y). |
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2.5.10. |
2yy' - |
X(y'2 + 4) = O. |
2.5.11. |
y = y,2 eyf • |
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2.5.12. |
y' + y - xy,2 = O. |
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2.5.13. |
y = xy' + y' + N. |
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2.5.14. |
xy' - |
y = lny'. |
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2.5.15. |
TIOCTPOUTb UHTerpaJIbHble KpUBble ypaBHeHUjI y = y' x + 1,. |
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y |
KOHTPOll bHASI PA60TA
BapMaHT 1
1. PernUTb .n;u<p<pepeHU;UaJIbHble ypaBHeHUjI:
a) x 2 dy + ydx = 0, y(l) = e; |
6) y' = 1 +1.;x |
2. PernuTb ypaBHeHue: y'(2x - |
y) = x + 2y. |
3. PernUTb ypaBHeHue: (x + y)y' - 1 = O.
80
4. PeIlIHTb yprumeHHe: (y3 + cos x) dx + (eY + 3xy2) dy = O.
5. 3a 30 ,n;Hei% pacnaJIOCb 50% nepBOHa'laJIbHOrOKOJIH'IecTBapa,n;H». Qepe3 CKOJIbKO BpeMeHH OCTaHeTC» 1% OT ero nepBOHa'laJIbHOrOKOJIH'IeCTBa,ecJIH CKOPOCTb pacna,n;a Pa,n;H» nponOpll;HOHaJIbHa ero KOJIH'IeCTBYB paccMaTpHBaeMbIi% MOMeHT?
BapMaHT 2
1. PeIlIHTb ,n;Hq,q,epeHll;HaJIbHbIe ypaBHeHH»:
a) y2y' + 2x - 1 = 0; |
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1 +y2 |
6) y' = -- 2' y(O) = 1. |
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l+x |
2. PeIlIHTb ypaBHeHHe: xy' - |
y = 2Jx2 + y2. |
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3. PeIlIHTb ypaBHeHHe: 3y' - |
2y = x 3y-2. |
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dx |
x +y2 |
O. |
4. PeIlIHTb ypaBHeHHe: y - |
-- 2 - dy = |
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Y
5. ABTOM06HJIb ,n;BIDKeTC» np»MOJIHHei%Ho co CKOPOCTbIO 30 M/C. 3a KaKoe BpeM» H Ha KaKOM paCCTO»HHH OH 6y,n;eT OCTaHOBJIeH TopM03aMH, eCJIH coIIpOTHBJIeHHe ,n;BIDKeHHIO IIOCJIe Ha'laJIaTopMOlKeHH» paBHO 0,3 ero Beca (g =
= 10 M/C2 )?
BapMaHT 3
1. PeIlIHTb ,LI;Hq,q,epeHll;HaJIbHbIe ypaBHeHH»:
a) ydx + ctgxdy,= 0, y (2;) = -2; 6) y'2x- y + 32x - y = O.
2. |
PeIlIHTb ypaBHeHHe: y dx = (x - |
y'xY) dy. |
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3. |
PeIlIHTb ypaBHeHHe: y' -' x ~ 1 = eX(x + 1). |
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4. |
1 |
3y2 ) |
2y |
PeIlIHTb ypaBHeHHe: ( 2 |
+ - 4 |
dx = 3" dy. |
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x |
x |
x |
5. |
TeJIo MacCbI m IIa,n;aeT BepTHKaJIbHO BHH3 IIO,n; ,n;ei%cTBHeM CHJIbI TIDKeCTH |
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H TOpM03»lll;ei% CHJIbl conpOTHBJIeHH» B03,n;yxa, npoIIOpll;HOHaJIbHoi% CKOPOCTH (K09q,q,Hll;HeHT npoIIOpll;HOHaJIbHOCTH k). Hai%TH 3aKOH H3MeHeHH» CKOpOCTH v IIa,n;eHH» TeJIa, eCJIH B MOMeHT BpeMeHH t = to v = Vo = O.
BapMaHT 4
1. PeIlIHTb ,n;Hq,q,epeHll;HaJIbHbIe ypaBHeHH»:
a) (1 + y2) dx - .jXdy = 0; 6) y' + ycosx = cos x, y(O) = 2.
81
2.PemHTb ypaBHeHHe: 3x2y' = y2 + 8xy + 4x2.
3.PemHTb ypaBHeHHe: xy' + y = xy2.
4. PemHTb ypaBHeHHe: (sin 2x - 2 cos(x + y)) dx - 2 cos(x + y) dy = O.
5. TeJIo ,n;BIDKeTCH IIPHMOJIHHeilHO C yCKopeHHeM, IIPOIIOPIJ;HOHaJIbHbIM IIPOH3Be,n;eHHIO CKOPOCTH ,n;BIDKeHHH v Ha BpeMH t. YCTaHoBHTb 3aBHCHMOCTb Me)K,D;y CKOPOCTbIO H BpeMeHeM, eCJIH IIpH t = 0 v = Vo.
BaplilaHT 5
1. PemHTb ,n;Hq,q,epeHIJ;HaJIbHbIe ypaBHeHHH:
a) y' + y + 7 = OJ |
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6) (..fiY + v'x)dy = y dx, y(O) = l. |
2. PemHTb ypaBHeHHe: |
xy' - |
y |
Y |
x |
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= ctg X . |
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3. PemHTb ypaBHeHHe: xy' - |
x 2 sinx = y. |
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4. PemHTb ypaBHeHHe: (5xy2 - |
x3 ) dx + (5x2y - y) dy = O. |
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5. TeMIIepaTypa BbIHYToro H3 IIe'!HxJIe6a B Te'!eHHe20 MHHyT IIOHIDKaeT-
CH OT 100° ,n;o 60°. TeMIIepaTypa B03,D;yxa 20°. Qepe3 CKOJIbKO BpeMeHH OT Ha'!aJIaOXJIa)K,n;eHHH TeMIIepaTypa xJIe6a 6y,n;eT 30°? (YKa3aHHe: CKOPOCTb OXJIa)K,n;eHHH TeJIa IIPOIIOPIJ;HOHaJIbHa pa3HocTH TeMIIepaTYP TeJIa H cpe,n;bI.)
§6. Lt1HTErpLt1POBAHLt1E ALt1(J)(J)EPEHU.Lt1AJlbHbIX YPABHEHLt1~ BbICWLt1X nOPHAKOB
AIII(jJ(jJepeH4I11anbHble ypaBHeHIIIH BToporo nopHAKa. OCHOBHble nOHHTIilH. TeopeMa cyw.eCTBOBaHIIIH
III ~IIIHCTBeHHOCTIil
F(x,y,y',y") = 0, |
(6.1) |
CBH3b1BaIOrn;ee Me:lK.rr.y co6oit He3aBHCHMYIO nepeMeHHYIO, HeH3BeCTHYIO <PYHKIJ;HIO
y(x), a TaK:lKe ee nepBble )l:Be npOH3BO)l:Hble y'(x) H y"(x), Ha3bIBaeTC:iI aurjjrjjepe'H,-
'4ua.l!'b'H,'btM ypa6'H,e'H,UeM 6mopo~o nOpRa'ICa. |
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ECJIH ypaBHeHHe (6.1) MO:lKHO 3anHcaTb B BH)l:e |
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y" = !(x, y, y'), |
(6.2) |
TO rOBOp:ilT, 'ITOOHO pa3pellieHO OTHOCHTeJIbHO BTOPOit npOH3BO)l:Hoit. MbI 6Y)l:eM HMeTb )l:eJIO TOJIbKO C TaKHMH ypaBHeHH:ilMH.
~3a)l:a'laOTblCKaHH:iI peIIIeHH:iI ypaBHeHH:iI (6.2), y)l:OBJIeTBOp:ilIOrn;ero 3a)l:aHHblM
Ha'laJIbHbIMYCJIOBH:ilM y(xo) = yo, y'(xo) = yb, r)l:e Xo, yo, yb - |
HeKOTopble '1HCJIa, |
Ha3bIBaeTC:iI 3aaa'l,efJ, KoUJ,u. |
~ |
82
~Pew,e1tUeM yprumeHHx (6.2) Ha3bIBaeTCX BCXKax ¢YHKU;HX Y = rp(x), KOTopax
npH nO,D;CTaHOBKe BMeCTe C y' H y" B 9TO ypaBHeHHe o6paru;aeT ero B TO:lK,D;eCTBO. fpa¢HK ¢YHKU;HH y = rp(x) B 9TOM CJIY'IaeHa3bIBaeTCX u1tmezpa.J!b1toit -X;pU60it. ~
~0614UM pew,e1tUeM ypaBHeHHx (6.2) Ha3bIBaeTCX ¢YHKU;HX y = rp(x, C 1 , C2),
3aBHcxru;ax OT ,D;BYX rrpOH3BOJIbHbiX rrOCTOXHHblX C 1 H C2 H TaKax, 'ITO:
1) |
OHa XBJIXeTCX pemeHHeM 9Toro ypaBHeHHX rrpH JIro6blX KOHKpeTHblX 3Haqe- |
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HHXX Cl H C2 ; |
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2) |
rrpH JIro6blX ,D;OrrycTHMbIX HaqaJIbHblX YCJIOBHXX |
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y(xo) = yo, |
y' (xo) = y~ |
(6.3) |
MO:lKHO |
rrO,D;06paTb TaKHe 3HaqeHHX |
C? H C~ rrOCTOXHHbIX, 'ITO ¢YHKU;HX |
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y = rp(x, C?, C~) 6Y,D;eT Y,D;OBJIeTBOpXTb 9THM HaqaJIbHblM YCJIOBHXM. |
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~ JIro6ax ¢YHKU;HX y = rp(x, C?, C~), rroJIyqaroru;axcx H3 o6ru;ero pemeHHX YPaBrrpH KOHKpeTHblx 3Ha'leHHXXrrOCTOXHHblX C1 H C2, Ha3bIBaeTCX 'l.acm-
1tUM pew,e1tUeM 9Toro ypaBHeHHx. ~
,I1;.nx ,D;H¢¢epeHU;HaJIbHOrO YPaBHeHHX BToporo rrOpX,D;Ka (6.2) HMeeT MeCTO TeopeMa cyru;ecTBoBaHHx H e,D;HHCTBeHHOCTH pemeHHx, aHaJIOrH'IHaXcooTBeTcTByroru;eil: TeopeMe ,D;JIX ypaBHeHHiI: rrepBoro rrOpX,D;Ka.
TeopeMa 2.2. |
EClllll |
cPyHKlIlIIll !(x, y, y') III ee |
yaCTHble |
npOlll3BOAHbie !~(x, y, y') |
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III !~I (x, y, y') |
HenpepblBHbl |
B |
HeKoTopoiii |
o611acTIll D, |
COAep>Kal.J..leiii |
TOYKY C |
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KOOpAIilHaTaMIll |
(xo, Yo, y~), |
TO |
CYl.J..leCTByeT |
III |
nplllTOM |
eAIIIHCTBeHHoe |
peweHllle |
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y = y(x) ypaBHeHlIIll |
(6.2), YAOBlleTBOplllOl.J..Iee |
HayallbHblM |
YCllOBlIIllM |
y(xo) = Yo, |
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y'(xo) = y~. |
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06ru;HiI: HHTerpaJI |
<I>(x,y,C1 ,C2) = 0 HJIH o6ru;ee |
pemeHHe y |
= rp(X,C1,C2 ) |
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ypaBHeHHX (6.2) rrpe,D;CTaBJIXeT co6oil: ceMeil:cTBo KPHBbIX, 3aBHcxru;HX OT ,D;BYX rrpoH3BOJIbHbiX rrOCTOXHHblX C 1 H C2. 3a,D;aqa KomH B TaKOM cJIyqae COCTOHT B orrpe,D;e- JIeHHH HHTerpaJIbHoil: KPHBOil: y = y(x), rrpoxo,D;xru;eil: '1epe3,D;aHHYro TOqKY (xo, yo) H HMeroru;eil: ,D;aHHblil: yrJIOBoil: K09¢¢HU;HeHT y~ KaCaTeJIbHoil: t (,D;aHHOe HarrpaBJIeHHe B ,D;aHHOil: TO'lKe(pHC. 8)), T. e. y' (xo) = y~ = tg a.
y = y(x)
x
Puc. 8
83
nOHIII>KeHllle nOp"AKa AIII~~epeHu.lllallbHbIX ypaBHeHllliii
B HeKOTOpblX '1acTHblXCJIY'IMXY)l;aeTCH rrOHH3HTb rrOpH)l;OK )l;H<p<pepeHIJ;HaJIbHOro yprumeHHH BTOpOro rrOpH)l;Ka.
3a'laCTYIOOHO B HTOre rrpHBO)l;HTCH K )l;H<p<pepeHIJ;HaJIbHOMY ypaBHeHHIO rrepBOrO rrOpH)l;Ka O)l;HOrO H3 H3Y'IeHHbIXpaHee THrrOB.
PacCMOTPHM HaH60Jlee THrrH'IHbleCJIY'IaH.
YpaBHeHMH BMACI '1/" = f{x)
HHTerpHpOBaHHeM 06eHx '1aCTeil:ypaBHeHHH y" = f(x) OHO rrpHBO)l;HTCH K YPaBHeHHIO rrepBoro rrOpH)l;Ka
y' = Jf(x) dx = F(x) + c1 •
IIoBTopHO HHTerpHpYH rrOJlY'IeHHOepaBeHCTBO, HaxO)l;HM o6IIIee pemeHHe HCXO)l;HOrO ypaBHeHHH:
AM~~epeH4ManbHble ypaBHeHMH F{x, y', yll) = 0, HBHO He cOAep)l(a~e
MCKOMOM ~YHK4MM Y
TaKHe ypaBHeHHH )l;OrrYCKaIOT rrOHH:lKeHHe rrOpH)l;Ka rrO)l;CTaHoBKoil: y' = p, y" =
= p'. ,I4>yrHMH CJIOBaMH, )l;aHHOe ypaBHeHHe paBHOCHJlbHO CHCTeMe )l;H<p<pepeHIJ;H-
aJIbHbIX YPaBHeHHiI: rrepBoro rrOpH)l;Ka
{y' =p,
F(x,p,p') = o.
AM~cJlepeH4ManbHble ypaBHeHMH F{y, y', yll) = 0, HBHO He cOAep)l(a~e
He3aBMcMMoM nepeMeHHoM x
YpaBHeHHH TaKOrO BH)l;a )l;OrrYCKaIOT rrOHH:lKeHHe rrOpH)l;Ka rrO)l;CTaHoBKoil: y' = = p = p(y) (<pOpMaJIbHOe OTCYTCTBHe aprYMeHTa x rr03BOJlHeT C'IHTaTbHeH3BeCTHYIO <PYHKIJ;HIO p <PYHKIJ;Heil: aprYMeHTa y), OTKY)l;a: y" = (P(y))' = p'(y) . y'(x) =
=p' 'p.
TaKHM o6pa30M, ypaBHeHHe F(y, y', y") = 0 PaBHOCHJlbHO CHCTeMe
{ y' =p,
F(y,p,p' p') = o.
ECJlH <PYHKIJ;HH F HBJlHeTCH O)l;HOPO)l;HOil: <PYHKIJ;Heil: CTerreHH k OTHOCHTeJlbHO rrepeMeHHbIX y, y' H y", T. e. F(x, ty, ty', ty") = t k • F(x, y, y', y"), TO )l;H<p<pepeHIJ;H-
aJIbHOe ypaBHeHHe F(x, y, y', y") = 0 )l;OrrYCKaeT rrOHH:lKeHHe rrOpH)l;Ka rrO)l;CTaHOB-
KOil:
y = eJp(x)dx,
r)l;e p(x) - HOBaH HeH3BeCTHaH <PYHKIJ;HH.
84
LIIHTerpMpOBaHMe AM(j>(j>epeHu.ManbHbIX ypaBHeHMiii nopHAKa BblWe BTOpOrO
IIpHeMhI, orIHcaHHble B rrpe,Ll;hI~m;eM rrYHKTe, MO)KHO paCrrpOCTpaHHTb Ha YPaBHeHHH 60JIee BbICOKHX rrOpH,LI;KOB.
06m;ee peIIIeHHe rrpocTeihrrero ,LI;H<p<pepeHII;HaJIbHOro ypaBHeHHH n-ro rrOpH,LI;Ka y(n) HaxO,Ll;HTCH n-KpaTHhIM HHTerpHpOBaHHeM <PYHKII;HH f(x) H CO,Ll;ep)KHT n rrpOH3BOJIbHhIX rrOCTOHHHhIX.
,I1;H<p<pepeHII;HaJIbHOe ypaBHeHHe BH,LI;a F(x, y(k), y(k+l), ... , y(n») = 0, He cO,Ll;ep-
)Kam;ee B HBHOM BH,LI;e HCKOMOfi <PYHKII;HH y, ,LI;OrrYCKaeT rrOHH)KeHHe rrOpH,LI;Ka rro,Ll;- CTaHOBKofi y(k) =p. ,I1;pyrHMH CJIOBaMH, ,LI;aHHOe ypaBHeHHe PaBHOCHJIbHO CHCTeMe
y(k) = p, |
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{ |
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(n-k)_ |
o. |
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, .. . ,p |
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F(x,p,p |
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,I1;H<p<pepeHII;HaJIbHOe ypaBHeHHe |
BH,LI;a F(y, y', y", ... , y(n») = 0, He CO,Ll;ep)Ka- |
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m;ee HBHO aprYMeHT x, ,LI;OrrYCKaeT rrOHH)KeHHe rrOpH,LI;Ka Ha e,Ll;HHHII;y rrO,Ll;CTaHOBKOfi
IIpH 3TOM (rro rrpaBHJIY ,LI;H<p<pepeHII;HpOBaHHH CJIO)KHofi <PYHKII;HH):
" dp dp dy , |
,,_ d (' |
) dy |
_ (p" |
P |
+ (p')2) |
P |
y = dx = dy . dx = P . p, |
Y -- p . p . -- |
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dy |
dx |
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HT.,LI;.
2.6.1.HatiTH 06rn;ee pemeHHe )l;H<p<pepeHll;HaJIbHoro ypaBHeHHfl
y" = __1_ + x - sinx.
1 +x2
Q IIHTerpHpYfl, IIOJIyqHM
y' = 1(1 : x2 + x - sin x) dx = arctg x + x; + cos x + C1 •
TIoBTopHoe HHTerpHpOBaHHe (1arctg x dx Ha,n:O 6paTh IIO qacTflM: arctg x =
=u, du = ~,v = x, dx = dv) IIPHBO)l;HT K OTBeTY:
l+x
y =1(arctg x + ~2 + cos X + Cl) dx =
= xarctgx + ~In(l + x 2) + x; + sin x + C1x + C2. •
Ha11.mu o6w,ue peUteHWI OaHH'b/,X ou!Jj!JjepeH'4ua//,'bH'b/,X ypa6HeHu11.:
2.6.2.y" = sin4x + 2x - 3.
2.6.3. |
y" = e5x + cos x - 2x3 • |
2.6.4. |
y" = xex 2 + 3- x . |
2.6.5. |
y" = 4cos4 X + 2sin2 ~ +..;x + 2. |
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2 |
85
2.6.6.HaihH qacTHoe pemeHHe ,l1.aHHOrO ,l1.H<p<pepeHIJ;H8JIbHOrO ypaBHe-: HHH, y,l1.0BJIeTBOpHIOm;ee 3a,l1.aHHbIM Haq8JIbHbIM YCJIOBHHM:
y" = (e2X + sin3x)x, y(O) = 1, y'(O) = l.
a CHaq8JIa HaXO,l1.HM o6m;ee pemeHHe. lfHTerpHpYH no qacTHM, HaXO,l1.HM
y' = !(e 2X + sin 3x)x dx =
[(e + Si:;X~~X= dv, |
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3 |
1 |
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du = dx |
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2X |
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v = 1e2x _1 cos3x |
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1 |
2x |
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1 |
3) 1 |
2x |
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1. 3 |
x |
+ G |
1· |
(6.4) |
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=x ( 2e |
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3 cos x - 4e |
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+ 9 sm |
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IIoBTopHoe HHTerpHpOBaHHe no qacTHM (npo,l1.eJIaitTe HY)l{HbIe BbIqHCJIeHHH) npHBO,l1.HT K o6m;eMY pemeHHIO:
1 |
2x |
1. 3) 1 2x |
2 |
cos |
3 |
x + |
G |
IX + |
G |
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(6.5) |
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y = x ( -e |
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B paBeHCTBax (6.4) H (6.5) nO,l1.CTaBHM x = 0, y' = 1, y = 1, oTKY,l1.a nOJIyqaeM CHCTeMY ypaBHeHHit OTHOCHTeJIbHO HeH3BeCTHbIX KOHCTaHT G1 H G2 :
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1 = -4I+ G , |
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{5G = 4' |
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{ |
1 2 |
+ G2 , |
¢} |
143 |
1 = - 4 - 27 |
G2 |
= 108' |
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Hait,l1.eHHbIe 3HaqeHHH nOCTOHHHbIX nO,l1.CTaBJIHeM B o6m;ee pemeHHe (6.5). IIoJIyqaeM HCKOMoe qacTHoe pemeHHe
y = x (le 2x _1 sin3x) _le2x _.1. cos3x + Qx + 143 |
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108 . |
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Haii,mu "I,aCmH'bte peUteHWI OaHH'btX oUfp!fiepeH'I.{Ua.lI)bH'btX ypa6HeHuii" yOo6.1/,e- m60p.fl1O'I4ue 3aOaHH'btM Ha"l,a.l/,'bH'btM YC.I/,06W1M:
2.6.7.y" = (x 2 + 7x + 9)eX, y(O) = 1, y' (0) = 4.
2.6.8.y" - 2(2x2 + 2x - 5) cos2x - 4(2x + 1) sin2x, y = 0, y'(O) = o.
2.6.9.y" = l- 32 + 2cosx - xsinx, y(l) = 1, y'(l) = O.
x
2.6.10. y" = (4x 3 + lOx2 + 2x + 2)e2x + 6 sin 3x + 9xcos3x, y(O) = 1, y(O)' = l.
2.6.11.PemHTb ,l1.H<p<pepeHIJ;H8JIbHOe ypaBHeHHe y" - y' ctgx = 2x sin x.
HaitTH TaK)l{e qaCTHOe pemeHHe, eCJIH y = 1, y' = 0 npH x = i'
a ,IJ,aHHoe ,l1.H<p<pepeHIJ;H8JIbHOe ypaBHeHHe BTOpOro nOpH,l1.Ka He CO,l1.ep)l{HT HBHO HCKOMYIO <PYHKIJ;HIO y, T. e. HMeeT BH,l1. F(x, y', y") = O. IIoJIo)l{HM y' = p,
TOr,l1.a y" = p'. IIoJIyqaeM ,l1.H<p<pepeHIJ;H8JIbHOe ypaBHeHHe nepBoro nOpH,l1.Ka p' - p ctg x = 2x sin x - JIHHeitHoe OTHOCHTeJIbHO HeH3BecTHoit <PyHKIJ;HH p = p(x). 06m;ee pemeHHe ~noro ypaBHeHHH Hait,l1.eM nO,l1.CTaHOBKoit p = U· v, p' = u'v + uv'. IIoJIyqaeM:
" |
. |
{v' - vctgx = 0, |
u v + uv - |
uvctgx = 2xsmx |
¢} |
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u'v = 2xsinx. |
86
113 nepBoro ypaBHeHH~ Haxo,n:HM In Ivl = In I sin xl, T. e. v = sin x. TIo,n:cTaBJI~~ BO BTopoe ypaBHeHHe, nOJIyqHM u' = 2x, oTKy,n:a U = x 2+Cl . CJIe,n:oBaTeJIbHO,
p = uv = (x 2+Cd sin x, T. e. y' = |
(x 2+Cl ) sin x. I1HTerpHpy~ 9TO paBeHcTBo, |
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Hali,n:eM 06rn;ee perneHHe Hcxo,n:Horo ypaBHeHH~ |
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y = - (x 2 + C l) cos X + |
2x sin x + 2 cos x + C2. |
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I1o,n:cTaBJI~~ B ,n:Ba nOCJIe,n:HHX paBeHcTBa HaqaJIbHbIe yCJIOBH~ x = |
~, y = 1, |
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y' = 0, nOJIyqaeM |
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1 = - |
11"2 |
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V2 |
11" |
V2 |
V2 |
+ C 2 . |
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( -16 |
+ C l |
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+ -2 |
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+ 2 . - 2 |
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Hali,n:eHHbIe 3HaqeHH~ C l = |
- ~~ H C2 = |
1 - |
V; (i + 2) no,n:CTaBJI~eM B |
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06rn;ee perneHHe. OTclO,n:a HCKOMoe qaCTHOe perneHHe |
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11" + 4 In |
(2 |
11"2 |
-2 |
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cosx. |
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y.. =2xsmx+I--- v2 - |
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-16 |
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C'!/'eJy1Ow,ue Ju!p!pepeH14Ua.JI,bHUe |
ypa6HeH'IJ.R pewumb noJcmaH06'1wiJ. y' = p: |
2.6.12. y" - ~y' = 2x3 • |
2.6.13. (x + l)y" = y' - 1. |
2.6.14.x 3 y"+x2y'-1=0. 2.6.15. y"+y'tgx-sin2x=0.
2.6.16. |
xy" - y' = x2ex . |
2.6.17. |
xy"lnx = y'. |
2.6.18. |
y" tg x - y' - 1 = O. |
2.6.19. |
xy" + y' + x = O. |
2.6.20.(1 + x 2)y" + 2xy' - x 3 = O. ,
2.6.21.HaihH 06rn;ee perneHHe ,n:H<p<pepeHI.J;HaJIbHoro ypaBHeHH~ y" tg Y =
=2(y')2. HaliTH TaK)I{e qacTHoe perneHHe, y,n:oBJIeTBOp~lOrn;ee HaqaJIbHbIM yCJIOBH~M y(l) = ~, y'(I) = -2.
Q ,Il;aHHoe ,n:H<p<pepeHI.J;HaJIbHOe ypaBHeHHe He co,n:ep)l{HT B ~BHOM BH,n:e aprYMeHTa x, T. e. HMeeT BH,n: F(y, y', y") = O. TIpHMeM B KaqeCTBe He3aBHCHMoli
rrepeMeHHoli y H BbInOJIHHM 3aMeHY y' = p = p(y). Tor,n:a y" = |
p . p', a HC- |
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Xo,n:Hoe ypaBHeHHe npHHHMaeT BH,n:: p . p' tg Y = 2p2. ECJIH P = |
0, TO y' = 0, |
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T. e. y = |
C. TIoCJIe COKparn;eHH~ Ha p :f. |
0 pernHM ,n:H<p<pepeHI.J;HaJIbHOe ypaB- |
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HeHHe nepBoro nop~.D:Ka p' tg Y = 2p. |
8TO ypaBHeHHe C pa3,n:eJI~IOlI.J;HMHC~ |
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rrepeMeHHbIMH. PernaeM ero cTaH,n:apTHbIM 06pa30M: |
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dp = 2cos y d |
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siny |
y, |
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T.e. lnipi = 2lnlsinyl + IniCll, C l |
:f. |
0, |
oTKy,n:a p = C l sin2 y (3aMeTHM, |
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'-ITOHali,n:eHHoe paHee perneHHe p = |
0 co,n:ep)l{HTC~ B nOJIyqeHHOM BbIproKe- |
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Hll.ll. - |
,n:OCTaTO'-IHOnOJIO)l{HTb C l = |
0). 3aMeHHM p Ha y' H pernHM ypaB- |
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HeHll.e y' = C l sin2 y, KOTopoe TaK)l{e ~BJI~eTC~ ypaBHeHHeM C pa3,n:eJI~IOrn;H-
dy
Mll.C~ nepeMeHHbIMH: - . - 2 - = C l dx, HJIH -ctgy = Clx + C2. TIOJIyqHJIH sm y
06rn;ee perneHHe Hcxo,n:Horo ypaBHeHH~ B He~BHOM BH,n:e. TIo,n:cTaBHM B Hero
87
H B BblpruKeHHe )J,JUI y' 3HaqeHHjI x = 1, y = i H |
y' = -2. 113 paBeHcTBa |
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-2 = Cl sin2 i |
HaXO,D;HM Cl = -4, a H3 paBeHcTBa - |
ctg i = Cl + C2 , yqH- |
TbIBajl, qTO Cl |
= -4, HaXO,D;HM C2 = 3. IIo,D;cTaBJIjIjI IIOJIyqeHHble 3HaqeHHjI |
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KOHCTaHT B o6m;ee perneHHe, KOTopoe 3arrHrneM B BH.n;e y = arcctg( -Cl X-C2),
HaXO,D;HM Tpe6yeMoe qacTHoe perneHHe y.. = arcctg(4x - 3). |
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2.6.22. |
HaitTH qaCTHOe perneHHe ,D;Hq,q,epeHn:HaJIbHOrO ypaBHeHHjI |
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(1 + yy')y" = (1 + (y')2)y', |
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a |
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y,D;OBJIeTBOpjlIOm;ee HaqaJIbHbIM YCJIOBHjlM y(O) = y'(O) = 1. |
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IIo,D;cTaHoBKa Y.' = P = p(y) H y" = P . p' |
rrpHBO,D;HT ,D;aHHOe ypaBHe- |
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HHe |
K BH,D;y (1 + py)p. p' = (1 + p2)p, OTKY,D;a |
p = 0, T.e. y = C, |
HJIH |
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p' |
= |
1 + p2 |
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+ py. IIoJIyqeHf:\oe ,D;Hq,q,epeHn:HaJIbHOe ypaBHeHHe He OTHOCHTCjI K |
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ypaBHeHHjlM rrepBoro rrOpjl,D;Ka H3BeCTHoro HaM THIIa. IIepeIIHrneM ero B BH,D;e
y' = |
1 + py |
1 |
--- 2' yqHTbIBM, qTO p' |
= , . IIOJIyqHM JIHHeitHoe (OTHOCHTeJIbHO y |
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l+p |
y |
H y') ,D;Hq,q,epeHn:HaJIbHOe ypaBHeHHe IIepBoro rrOpjl,D;Ka, KOTopoe MO)l{HO pernHTb IIO,D;CTaHoBKoit y Ero o6m;ee perneHHe HMeeT BH,D; (Hait,D;HTe ero caMOCTOjlTeJIbHO)
+Cl).
Terrepb OCTaeTCjI pernHTb ,D;Hq,q,epeHI.I;HaJIbHOe ypaBHeHHe IIepBoro rropjl.n;Ka
y = VI + (y')2 ( |
y' |
+ Cl), |
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VI + |
(y')2 |
He pa3perneHHoe OTHOCHTeJIbHO IIPOH3BO,D;HOit y'. Ho B 06m;eM BH,D;e pernHTb ero ,D;OCTaTOqHO XJIOrrOTHO. O,D;HaKO, TaK KaK HaM HY)l{HO HaitTH qacTHoe perneHHe HCXO,D;HOrO ypaBHeHHjI, TO BOCrrOJIb3yeMcjI HaqaJIbHbIMH YCJIOBHjlMH ,D;JIjI orrpe,D;eJIeHHjI IIOCTOjlHHOit Cl, IIOJIaraji B IIOCJIe,D;HeM paBeHCTBe y = 1 H y' = 1. IIpHxo,D;HM K paBeHcTBY
1=J2(~+Cl)'
H3 KOToporo Cl = O. TeM caMbIM, HaM ,D;OCTaTOqHO pernHTb ypaBHeHHe y = y',
OTKY,D;a y = Cex . IIoJIarM 3,D;eCb x = 0, y = 1, HaxO,D;HM C = 1. TaKHM o6pa30M y.. = eX - HCKOMoe qacTHoe perneHHe. •
Hatimu o6'l4ue pemeHUJI cAeay1O'l4UX aug)(pepeHv,uaA'bHUX ypaaHeHuti, a ma.M, eae Y'K:a3aHU Ha"taA'bHUe YCAOaUJI, Hatimu coomaemcmaY1O'l4ee "tacmHoe pemeHue:
2.6.23. y"y3 = 1. |
2.6.24. yy" - (y')2 - 1 = O. |
2.6.25.1 + (y')2 - 2yy" = O. 2.6.26. 2yy" - 3(y')2 = 4y2.
2.6.27.y" = y'(1 + (y')2).
2.6.28.y" = y'lny', y(O) = 0, y'(O) = 1.
88
2.6.29.y" + y'V(y')2 -1 = 0, yen") = 0, y'(7r) =-1.
2.6.30.3y'y" = 2y, yeO) = y'(O) = 1.
2.6.31.y" = 2y3, yeO) = 0, y' (0) = 1.
2.6.32.npOHHTerpHpoBaTb AH<p<pepeHIJ;HaJIbHOe ypaBHeHHe BTOp01'O IIO-
pjl,II.Ka xy' (yy" - (y')2) = y(y')2 + x4 y3.
a nepenHIIIeM ypaBHeHHe B BHAe
xy' (yy" - (y')2) _ y(y')2 _ X4y3 = 0,
rrOCJIe 'Iero0603Ha'IHM'Iepe3F(x, y, y', y") JIeBYIO 'IacTbnOJIY'IeHHOrOpaBeHCTBa. EcJIH 3aMeHHTb y, y', y" Ha ty, ty', ty", COOTBeTCTBeHHO, TO IIpHXOAHM K paBeHCTBY
F(x, ty, ty', ty") = t 3 [xy' (yy" - |
(y')2) - y(y')2 - X4y3] = t 3 F(x, y, y', y"). |
2ho 03Ha'iaeT,'ITO<PYHKIJ;HjI F - |
OAHOPOAHM (TpeTbeti CTeIIeHH, k = 3) H B |
TaKOM CJIY'IaeCOOTBeTCTBYIOrn;ee ypaBHeHHe AOIIycKaeT IIOHillKeHHe IIOpjlAKa rroAcTaHoBKoti Y = eJ p dx, rAe P = HeH3BeCTHaji <PYHKIJ;HjI OT x.
OTCIOAa y' = peJ p y" = (p' +p2)eJ p nOCJIe COOTBeTCTBylOrn;HX 3aMeH H dx.
dx, °
COKparn;eHHjI Ha e 3 Jp dx f IIpHXOAHM K AH<p<pepeHIJ;HaJIbHOMY ypaBHeHHIO rrepBoro nOpjlAKa OTHOCHTeJIbHO p
HJIH
(ilpH 3TOM MbI TepjleM peIIIeHHe y == 0, KOTopoe IIOTOM HaAO Ao6aBHTb K OTBeTY). nOJIY'IHJIHypaBHeHHe BepHYJIJIH, KOTopoe MO)l{HO peIIIHTb (IIpeAJIaraeM CAeJIaTb 3TO caMOCTOjlTeJIbHo) IIOACTaHoBKoti p = uv. Ero o6rn;ee peIIIeHHe
HMeeT BHA
P=XVX2 +C1 •
nOCKOJIbKY y = eJp dx, TO HaxOAHM CHa'IaJIa
Jpdx = JXVX2 + C1 dx = lV(x2 + CJ)3 + C2,
a 3aTeM H o6rn;ee peIIIeHHe HCXOAH01'OAH<p<pepeHIJ;HaJIbHOrO ypaBHeHHjI (3a BbI'IeTOM'IaCTHOropeIIIeHHjI y = O)HMeeT BHA
C3 > 0.
Y'IHTbIBM,'ITOIIpH C3 = °KaK pa3 nOJIY'IaeTCjIIIOTepjlHHOe 'IaCTHOe peIIIeHHe y = 0, npHXOAHM K OKOH'IaTeJIbHOMYOTBeTY: y = C3 . etV(X2 +C2 )3,
C3 ~O. |
• |
Pew,um'b iJu!p!pepeHv,Ua.J!'bH'bI.e ypa6'lteH'l.I.R.:
2.6.33.x 2yy" = (y - Xy')2. 2.6.34. 2yy" - 3(y')2 = 4y2.
2.6.35. HatiTH 'IaCTHOepeIIIeHHe AH<p<pepeHIJ;HaJIbHo1'OypaBHeHHjI TpeTbe-
1'0 nOPMKa y'" = 16 cos3 2x + eX - 1, YAOBJIeTBOpjllOrn;ee Ha'IaJIbHbIM YCJIOBHjlM yeO) = -1, y'(O) = -!, y"(O) = 3.
89
