MATEMAATILINE ANALÜÜS II - Tallinna Tehnikaülikool
MATEMAATILINE ANALÜÜS II - Tallinna Tehnikaülikool
MATEMAATILINE ANALÜÜS II - Tallinna Tehnikaülikool
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186 PEATÜKK 3. INTEGRAALARVUTUS<br />
Näide 2. Leiame kahe kera x 2 + y 2 + z 2 ≤ 1 ja x 2 + y 2 + (z − 1) 2 ≤ 1<br />
ühisosa ruumala.<br />
Skitseerime need kerad ja nende ristl~oike xz-tasandiga<br />
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1<br />
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z ✻<br />
x 2 + y 2 + (z − 1) 2 = 1<br />
2<br />
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x 2 + y 2 + z 2 = 1<br />
ψ = π 3<br />
✲<br />
y<br />
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2<br />
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ρ = 2 cos ψ<br />
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pr xz Ω<br />
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1<br />
ρ = 1<br />
ψ = π 3<br />
Et keha on sümmeetriline z-telje suhtes, siis piisab uurida selle keha ristl~oiget<br />
xz-tasandiga. Kerade ühisosa on koonusega ψ = π/3 jaotatav kahte ossa. Kuna<br />
ning<br />
x 2 + y 2 + z 2 = 1 ←→ ρ = 1<br />
x 2 + y 2 + (z − 1) 2 = 1 ←→ ρ = 2 cos ψ,<br />
siis Lause 3.5.1 viienda osa ja valemi (3.7.6) abil saame (miks?)<br />
∫∫∫<br />
V Ω = dxdydz =<br />
0<br />
Ω<br />
∫2π<br />
∫π/3<br />
= dϕ dψ<br />
0<br />
= 1 ∫2π<br />
∫<br />
dϕ<br />
3<br />
0<br />
π/3<br />
0<br />
∫ 1<br />
0<br />
∫2π<br />
∫π/2<br />
ρ 2 sin ψ dρ + dϕ dψ<br />
sin ψ dψ + 8 ∫2π<br />
∫<br />
dϕ<br />
3<br />
0<br />
0<br />
π/2<br />
π/3<br />
π/3<br />
∫<br />
2 cos ψ<br />
0<br />
cos 3 ψ sin ψdψ =<br />
ρ 2 sin ψ dρ =<br />
✲x<br />
= 2π 3<br />
∫<br />
π/3<br />
0<br />
sin ψ dψ + 16π<br />
3<br />
∫π/2<br />
π/3<br />
= − 2π ∣ ∣∣∣<br />
π/3<br />
3 cos ψ − 4π 3 cos4 ψ<br />
∣<br />
0<br />
cos 3 ψ sin ψdψ =<br />
π/2<br />
π/3<br />
= − 2π 3 cos π 3 + 2π 3 + 4π 3 cos4 π 3 = 5π<br />
12 . ♦<br />
=