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Çâ³äñè âèïëèâຠâëàñòèâ³ñòü 7 äëÿ ñóìè. Àíàëîã³÷íî äîâîäèòüñÿ<br />
âëàñòèâ³ñòü 7 äëÿ ð³çíèö³. ×èòà÷åâ³ ïðîïîíóºìî<br />
öå çðîáèòè ñàìîñò³éíî.<br />
8. ßêùî ∀x∈[à, b]: f(õ) ≥ 0 (à < b), òî î÷åâèäíî, ùî<br />
b<br />
( ) 0.<br />
∫ f x dx≥<br />
9. ßêùî ∀x∈[à, b]: f(õ) ≤ g(x) (a < b), òî<br />
b<br />
a<br />
∫f( x) dx ≤ ∫ g( x)<br />
dx .<br />
a<br />
b<br />
a<br />
Öÿ âëàñòèâ³ñòü âèïëèâຠ³ç âëàñòèâîñò³ 7 ³ ïîïåðåäíüî¿.<br />
10. ßêùî ∀x∈[à, b]: m ≤ f(õ) ≤ M (à < b), òî<br />
b<br />
( − ) ≤ ( ) ≤ ( − )<br />
mb a ∫ fxdx Mb a.<br />
a<br />
Öÿ âëàñòèâ³ñòü âèïëèâຠ³ç âëàñòèâîñòåé 6 ³ 9.<br />
Ó âèïàäêó, êîëè f(õ) > 0, öÿ âëàñòèâ³ñòü äîáðå ³ëþñòðóºòüñÿ<br />
ãåîìåòðè÷íî (ðèñ. 9.7): ïëîùà êðèâîë³í³éíî¿ òðàïåö³¿<br />
àÀÂb íå ìåíøà, í³æ ïëîùà ïðÿìîêóòíèêà àÀ 1  1 b, ³ íå á³ëüøà,<br />
í³æ ïëîùà ïðÿìîêóòíèêà àÀ 2  2 b.<br />
b<br />
a<br />
( ) = ( ξ)( − ).<br />
∫ f x dx f b a<br />
Äîâåäåííÿ. Îñê³ëüêè f(õ) íåïåðåðâíà íà ñåãìåíò³<br />
[a, b], òî âîíà äîñÿãຠíà öüîìó ñåãìåíò³ ñâîãî íàéìåíøîãî ³<br />
íàéá³ëüøîãî çíà÷åííÿ m, Ì. Òîä³<br />
àáî<br />
b<br />
( − ) ≤ ( ) ≤ ( − )<br />
mb a ∫ fxdx Mb a,<br />
a<br />
1<br />
b<br />
m≤<br />
∫ f( x)<br />
dx ≤ M.<br />
b−<br />
a a<br />
1<br />
Âåëè÷èíà µ= b<br />
fxdx ( )<br />
b a<br />
∫ íàçèâàºòüñÿ ñåðåäí³ì çíà÷åííÿì<br />
− a<br />
ôóíêö³¿ f(õ) íà ñåãìåíò³ [a, b]. Âíàñë³äîê íåïåðåðâíîñò³<br />
ôóíêö³¿ íà [à, b] ³ñíóº òàêà òî÷êà ξ º [à, b], ùî f(ξ) =µ, òîáòî<br />
1<br />
b<br />
f() ξ = ∫ f() x dx,<br />
b−<br />
a a<br />
ùî é òðåáà áóëî äîâåñòè.<br />
Ãåîìåòðè÷íî öÿ òåîðåìà ³ëþñòðóºòüñÿ íà ðèñ. 9.8. Ïëîùà<br />
êðèâîë³í³éíî¿ òðàïåö³¿ àÀÂb äîð³âíþº ïëîù³ ïðÿìîêóòíèêà<br />
àÀ 1 Âb ç îñíîâîþ b – a ³ âèñîòîþ f(ξ).<br />
Ðèñ. 9.7<br />
Òåîðåìà 9.3.1 (ïðî ñåðåäíº çíà÷åííÿ ôóíêö³¿). ßêùî<br />
ôóíêö³ÿ f(õ) íåïåðåðâíà íà ñåãìåíò³ [a, b], òî íà öüîìó ñåãìåíò³<br />
³ñíóº òàêà òî÷êà ξ, ùî áóäå ñïðàâåäëèâà ð³âí³ñòü<br />
Ðèñ. 9.8<br />
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