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ßêùî ³ñíóþòü îêðåìî ñê³í÷åíí³ ãðàíèö³<br />
lim<br />
c−ε1<br />
( ) lim ∫ ( )<br />
∫ f x dx, f x dx,<br />
ε1→0 a<br />
ε2→ 0c+ε<br />
2<br />
òî ³íòåãðàë ó ë³â³é ÷àñòèí³ ôîðìóëè (9.6.9) íàçèâàºòüñÿ<br />
çá³æíèì, à ÿêùî õî÷à á îäíà ç öèõ ãðàíèöü íå ³ñíóº àáî º<br />
íåñê³í÷åííîþ — ðîçá³æíèì.<br />
ßêùî îñîáëèâèìè º ò³ëüêè òî÷êè à ³ b, òî çà îçíà÷åííÿì<br />
b c b<br />
( ) = ( ) + ( ) ,<br />
b<br />
∫f x dx ∫f x dx ∫ f x dx<br />
(9.6.10)<br />
a a c<br />
äå ñ — äîâ³ëüíà òî÷êà ³íòåðâàëó (à, b). ²íòåãðàë ó ë³â³é<br />
÷àñòèí³ ôîðìóëè (9.6.10) áóäå çá³æíèì, ÿêùî îáèäâà ³íòåãðàëè<br />
ó ïðàâ³é ¿¿ ÷àñòèí³ çá³æí³.<br />
Ç ãåîìåòðè÷íî¿ òî÷êè çîðó, ³íòåãðàë (9.6.8) òàêîæ, ÿê ³<br />
íåâëàñíèé ³íòåãðàë ² ðîäó, âèðàæຠïëîùó íåñê³í÷åííî¿ ô³ãóðè<br />
(ðèñ. 9.13).<br />
Ðîçâ’ÿçàííÿ. Ó äàíîìó ïðèêëàä³ îñîáëèâîþ º òî÷êà<br />
õ = 1. Òîä³ ìàºìî:<br />
dx<br />
dx<br />
−ε<br />
π<br />
= = ( arcsin x) = ( arcsin( 1−ε ))<br />
= arcsin1 = .<br />
1−x<br />
1−x<br />
2<br />
1 1−ε<br />
1<br />
∫ lim ∫ lim lim<br />
2 0 2 0<br />
0<br />
0 ε→ 0<br />
ε→ ε→0<br />
²íòåãðàë çá³ãàºòüñÿ.<br />
Ïðèêëàä 9.6.10. Äîñë³äèòè íà çá³æí³ñòü ³ ó âèïàäêó çá³æíîñò³<br />
îá÷èñëèòè ³íòåãðàë:<br />
2<br />
∫<br />
dx<br />
( x − )<br />
−1 3<br />
2<br />
1<br />
Ðîçâ’ÿçàííÿ. Ó äàíîìó ïðèêëàä³ ï³ä³íòåãðàëüíà<br />
ôóíêö³ÿ ìຠíåñê³í÷åííèé ðîçðèâ ó òî÷ö³ x = 1, ÿêà çíàõîäèòüñÿ<br />
óñåðåäèí³ â³äð³çêà ³íòåãðóâàííÿ [–1, 2]. Çàñòîñóºìî<br />
ôîðìóëó (9.6.9):<br />
dx dx dx<br />
2 1−ε1<br />
2<br />
3<br />
1<br />
∫ = lim ∫ + lim ∫ = lim 3 x − 1 +<br />
−1 3<br />
2 ε→+ 1 0<br />
− 1 3<br />
2 ε2→+ 0<br />
1+ε<br />
3<br />
2 ε→+ 1 0<br />
( x−1 2<br />
) ( x−1) ( x−1)<br />
.<br />
1−ε<br />
−1<br />
3 3 3<br />
( 1 ) ( 2 ) ( )<br />
2<br />
+ lim 3 x − 1 = 3 lim −ε − − 2 + 3 lim 1 − ε = 3 2 + 1 .<br />
3 3 3<br />
ε2→+ 0 1+ε<br />
ε1→+ 0 ε2→+<br />
0<br />
2<br />
²íòåãðàë çá³ãàºòüñÿ.<br />
Ïðèêëàä 9.6.11. Äîñë³äèòè íà çá³æí³ñòü<br />
Ðèñ. 9.13<br />
Ïðèêëàä 9.6.9. Äîñë³äèòè íà çá³æí³ñòü ³ ó âèïàäêó çá³æíîñò³<br />
îá÷èñëèòè ³íòåãðàë<br />
1<br />
∫<br />
0 1<br />
dx<br />
.<br />
2<br />
− x<br />
e<br />
dx<br />
∫ . (9.6.11)<br />
1 x ln x<br />
Ðîçâ’ÿçàííÿ. Îñîáëèâîþ º òî÷êà õ = 1, îñê³ëüêè<br />
ln1 = 0. Ìàºìî:<br />
( ln x)<br />
e<br />
dx<br />
e d<br />
e<br />
∫ = lim ∫ = lim( ln ( ln x)<br />
) = lim( − ln ( ln ( 1+ε )))<br />
=+∞.<br />
1 xln<br />
x ε→01+ε<br />
ln x ε→0 1+ε<br />
ε→0<br />
Îòæå, ³íòåãðàë (9.6.11) ðîçá³æíèé.<br />
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