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π<br />
π<br />
π<br />
2<br />
⎛ 1 ⎞<br />
∫sin ∫( 1 cos 2 ) ⎜ sin 2 ⎟<br />
0 0 ⎝ ⎠0<br />
2<br />
π π π<br />
V =π xdx = − x dx = x − x = .<br />
2 2 2 2<br />
ÂÏÐÀÂÈ<br />
Ðèñ. 9.25<br />
9.22. Îá÷èñëèòè îá’ºì ò³ëà, óòâîðåíîãî îáåðòàííÿì ô³ãóðè,<br />
ÿêà îáìåæåíà ë³í³ÿìè:<br />
1) y 2 = px, x = a íàâêîëî îñ³ Ox;<br />
2 2<br />
x y<br />
2) + = 1<br />
2 2 íàâêîëî îñ³ Oy;<br />
a b<br />
3) 2y = x 2 , 2x +2y – 3 = 0 íàâêîëî îñ³ Ox;<br />
4) y =4–x 2 , y = 0 íàâêîëî ïðÿìî¿ x =3.<br />
9.9. ÏËÎÙÀ ÏÎÂÅÐÕͲ Ò²ËÀ ÎÁÅÐÒÀÍÍß<br />
9.9.1. Âèïàäîê îáåðòàííÿ êðèâî¿, ÿêà çàäàíà ð³âíÿííÿì<br />
y=f(x), x∈ [a, b]<br />
Íåõàé ãðàô³ê íåïåðåðâíî äèôåðåíö³éîâíî¿ ôóíêö³¿<br />
y = f(x), x∈[a, b] (f(x) ≥ 0) îáåðòàºòüñÿ íàâêîëî îñ³ Îõ. Òîä³<br />
ìîæíà ïîêàçàòè, ùî ïëîùà ïîâåðõí³ ò³ëà, óòâîðåíîãî òàêèì<br />
÷èíîì, ³ñíóº ³ âîíà çíàõîäèòüñÿ çà ôîðìóëîþ<br />
( ) ( ′( )) 2<br />
b<br />
S = 2π ∫ f x 1+<br />
f x dx. (9.9.1)<br />
a<br />
Ïðèêëàä 9.9.1. Îá÷èñëèòè ïëîùó ïîâåðõí³ øàðîâîãî ïîÿñó<br />
âèñîòè H (÷àñòèíà ñôåðè, ÿêà âèð³çàíà äâîìà ïàðàëåëüíèìè<br />
ïëîùèíàìè, ùî ðîçòàøîâàí³ îäíà â³ä îäíî¿ íà â³äñòàí³<br />
H), ÿêùî ðàä³óñ ñôåðè äîð³âíþº R.<br />
Ðîçâ’ÿçàííÿ. Ïîâåðõíþ øàðîâîãî ïîÿñó ìîæíà ðîçãëÿíóòè<br />
ÿê ïîâåðõíþ ò³ëà, ÿêó óòâîðåíî ïðè îáåðòàíí³ äóãè<br />
2 2<br />
êîëà y = R − x , äå a ≤ x ≤ b, b – a = H, íàâêîëî îñ³ Îõ, (÷èòà-<br />
÷åâ³ ïðîïîíóºìî çîáðàçèòè öåé ôàêò â³äïîâ³äíèì ðèñóíêîì).<br />
Îñê³ëüêè, f′ ( x) =<br />
−x<br />
2 2 , òî ( ( )) 2 R<br />
1 + f′<br />
x = ,<br />
2 2 ³<br />
R − x<br />
R − x<br />
çã³äíî ç ôîðìóëîþ (9.9.1) áóäåìî ìàòè<br />
b<br />
2 2 R<br />
b<br />
S = 2π∫<br />
R −x ⋅ dx = 2π R∫dx = 2πR( b− a)<br />
= 2πRH<br />
.<br />
a<br />
2 2<br />
R − x<br />
a<br />
Îòæå, ïëîùà ïîâåðõí³ øàðîâîãî ïîÿñó âèñîòè H îá÷èñëþºòüñÿ<br />
çà ôîðìóëîþ S = 2π RH .<br />
Çîêðåìà, ïëîùó ïîâåðõí³ ñôåðè ðàä³óñà R ìîæíà îòðèìàòè<br />
øëÿõîì ãðàíè÷íîãî ïåðåõîäó îñòàííüî¿ ð³âíîñò³ ïðè<br />
2<br />
H → R: S = 4π R .<br />
ñô.<br />
9.9.2. Âèïàäîê îáåðòàííÿ êðèâî¿, ÿêà çàäàíà ïàðàìåòðè÷íî<br />
ßêùî êðèâà çàäàíà ïàðàìåòðè÷íî:<br />
x=ϕ () t , y =ψ()<br />
t ( α≤t≤β,<br />
)<br />
äå ϕ, ψ — íåïåðåðâíî äèôåðåíö³éîâí³ ôóíêö³¿ íà ñåãìåíò³<br />
ϕα = ϕβ = b , òî ³ç ôîðìóëè (9.9.1) âèïëèâຠòàêà<br />
[α, β], ( ) a,<br />
( )<br />
β<br />
() ( ′()) ( ′())<br />
2 2<br />
S = 2π∫ ψ t ϕ t + ψ t dt . (9.9.2)<br />
α<br />
Ïðèêëàä 9.9.2 Îá÷èñëèòè ïëîùó S ïîâåðõí³, îòðèìàíî¿<br />
x= a t− sin t , y= a 1−cos t ,<br />
øëÿõîì îáåðòàííÿ öèêëî¿äè ( ) ( )<br />
0≤ t ≤2π, íàâêîëî îñ³ Îõ.<br />
330 331