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Ïðè ðîçâ’ÿçàíí³ ñèñòåìè (3.2.2) ìîæëèâ³ òàê³ âèïàäêè.<br />
1) ∆≠0. Òîä³ ñèñòåìà (3.2.3) ìຠºäèíèé ðîçâ’ÿçîê ³ íåâ³äîì³<br />
õ 1 òà x 2 çíàõîäÿòüñÿ çà äîïîìîãîþ òàêèõ ôîðìóë<br />
∆1 ∆2<br />
x1 = , x2<br />
=<br />
∆ ∆ ; (3.2.4)<br />
2) ∆ = 0 ³ ïðèíàéìí³ îäèí ³ç âèçíà÷íèê³â ∆ 1 (àáî ∆ 2 ) â³äì³ííèé<br />
â³ä íóëÿ. Òîä³ õî÷à á îäíå ç ð³âíÿíü ñèñòåìè áóäå<br />
ñóïåðå÷ëèâèì. Öå îçíà÷àº, ùî ñèñòåìà (3.2.3) íå ìຠðîçâ’ÿçêó,<br />
òîáòî íåñóì³ñíà.<br />
3) ∆=0 ³ ∆ 1 = 0, ∆ 2 = 0. Òîä³ ñèñòåìà (3.2.3) íåâèçíà÷åíà ³<br />
ìຠíåñê³í÷åííó ìíîæèíó ðîçâ’ÿçê³â, îñê³ëüêè â öüîìó âèïàäêó<br />
âîíà ìຠâèãëÿä:<br />
⎧0⋅ x1<br />
= 0;<br />
⎨<br />
⎩0 ⋅ x2<br />
= 0.<br />
Çàóâàæåííÿ. Ó âèïàäêó 3) êîåô³ö³ºíòè a ij (i =1,2;<br />
j = 1,2) ñèñòåìè ïðîïîðö³éí³ (ïåðåâ³ðòå!), òîáòî ìຠì³ñöå<br />
ïîäâ³éíà ð³âí³ñòü<br />
a21 a22 b2<br />
= = =λ.<br />
a a b<br />
11 12 1<br />
Ïåðåéäåìî òåïåð äî äîñë³äæåííÿ á³ëüø çàãàëüíîãî âèïàäêó.<br />
3.3. ÌÅÒÎÄÈ ÐÎÇÂ’ßÇÓÂÀÍÍß ÑÈÑÒÅÌÈ n ÀËÃÅ-<br />
ÁÐÀ¯×ÍÈÕ Ð²ÂÍßÍÜ Ç n ÍÅ<strong>²</strong>ÄÎÌÈÌÈ<br />
3.3.1. Ìàòðè÷íèé ìåòîä<br />
Äëÿ òîãî ùîá îòðèìàòè ðîçâ’ÿçîê ÑËÀÐ (3.1.1) ïðè<br />
m = n ó çàãàëüíîìó âèãëÿä³, ïðèïóñòèìî, ùî êâàäðàòíà ìàòðèöÿ<br />
À ñèñòåìè (3.1.1) íåâèðîäæåíà, òîáòî A ≠ 0 . Ó öüîìó<br />
âèïàäêó ³ñíóº îáåðíåíà ìàòðèöÿ (äèâ. òåîðåìó 2.5.1).<br />
 ìàòðè÷í³é ôîðì³ âèõ³äíà ñèñòåìà ìຠâèãëÿä (3.1.3).<br />
Ïîìíîæèìî îáèäâ³ ÷àñòèíè ð³âíÿííÿ (3.1.3) íà À -1 çë³âà:<br />
À -1 Àõ = À -1 b, îñê³ëüêè À -1 À = Å ³ Åõ = õ, îòðèìàºìî<br />
õ = À -1 b. (3.3.1)<br />
Ïðèêëàä 3.3.1. Ðîçâ’ÿçàòè ìàòðè÷íèì ñïîñîáîì ñèñòåìó<br />
ð³âíÿíü<br />
⎧x −2x − x =−2 ⎛1 −2 −1 ⎞ ⎛−2⎞<br />
1 2 3<br />
⎪ ⎜ ⎟ ⎜ ⎟<br />
⎨3x1 + x2 + 2x3<br />
= 3 A= ⎜<br />
3 1 2<br />
⎟<br />
b=<br />
⎜<br />
3<br />
⎟<br />
.<br />
⎪<br />
x1 + 2x2 + 2x3<br />
= 3 ⎜1 2 2⎟ ⎜ 3⎟<br />
⎩<br />
⎝ ⎠ ⎝ ⎠<br />
Ó ïðèêëàä³ 2.5.1 äëÿ äàíî¿ ìàòðèö³ À çíàéäåíî ¿¿ îáåðíåíó.<br />
Îòæå,<br />
⎛x1<br />
⎞ ⎛−2 2 −3⎞⎛− 2⎞ ⎛4+ 6−9 ⎞ ⎛ 1⎞<br />
⎜ ⎟ 1⎜ ⎟⎜ ⎟ ⎜ ⎟ ⎜ ⎟<br />
x2 = 4 3 5 3 8 9 15 2 x1 1, x2 2, x3<br />
1<br />
1<br />
− −<br />
⎟⎜ = + − = ⇒ = = =− .<br />
⎜x<br />
⎟ ⎜<br />
3<br />
5 −4 7⎟⎜ 3⎟ ⎜−10 − 12 + 21⎟ ⎜−1<br />
⎟<br />
⎝ ⎠ ⎝ ⎠⎝ ⎠ ⎝ ⎠ ⎝ ⎠<br />
3.3.2. Ìåòîä âèçíà÷íèê³â (ïðàâèëî Êðàìåðà 1 )<br />
ßê ³ ðàí³øå, ðîçãëÿäàºìî ñèñòåìó n ð³âíÿíü ç n íåâ³äîìèìè<br />
â ïðèïóùåíí³, ùî ìàòðèöÿ À íåâèðîäæåíà. Çíàõîäæåííÿ<br />
ðîçâ’ÿçê³â ó ðîçãëÿäóâàí³é ñèñòåì³ ì³ñòèòüñÿ â òàê³é<br />
òåîðåì³.<br />
Òåîðåìà 3.3.1. ßêùî âèçíà÷íèê ∆ ñèñòåìè n ð³âíÿíü ç<br />
n íåâ³äîìèìè â³äì³ííèé â³ä íóëÿ, òî ñèñòåìà ñóì³ñíà ³ ìàº<br />
ºäèíèé ðîçâ’ÿçîê. Öåé ðîçâ’ÿçîê äàºòüñÿ òàêèìè çíà÷åííÿìè<br />
øóêàíèõ íåâ³äîìèõ:<br />
∆i<br />
xi<br />
= , i = 1, n , (3.3.2)<br />
∆<br />
äå ∆ i — âèçíà÷íèê, îòðèìàíèé ³ç ∆ çàì³íîþ â íüîìó i-ãî<br />
ñòîâïöÿ ñòîâïöåì â³ëüíèõ ÷ëåí³â b 1 , b 2 ,…, b n .<br />
Ôîðìóëè (3.3.2) îòðèìàëè íàçâó ôîðìóë Êðàìåðà.<br />
Äîâåäåííÿ. Îáåðíåíà ìàòðèöÿ áóäóºòüñÿ çà ôîðìóëîþ<br />
(2.5.2) ³ ìຠâèä:<br />
1 1<br />
A - = × °<br />
A A,<br />
äå à º ìàòðèöåþ, ÿêà ñîþçíà äî ìàòðèö³ A. Îñê³ëüêè<br />
åëåìåíòè ìàòðèö³ à ÿâëÿþòü ñîáîþ àëãåáðà¿÷í³ äîïîâíåííÿ<br />
1<br />
Êðàìåð Ãàáð³åëü (1704 – 1752) — øâåéöàðñüêèé ìàòåìàòèê.<br />
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