- 668 名前:132人目の素数さん [2022/09/23(金) 19:44:36.14 ID:N15NgvLO.net]
- >>495
(i)回転体をx=t(-1/2≦t<0,1<t≦3/2)で切った断面はドーナツ型で、 体積=2π〔∫[t=-1/2→0][√3/2+√{1-(1/2-t)^2}]^2-∫[t=1→3/2][√3/2-√{1-(1/2-t)^2}]^2〕 =4π√3∫[t=-1/2→0]√{1-(1/2-t)^2}dt 1/2-t=cosθとおくと-dt=-sinθdθ dt=sinθdθ 体積=2π√3∫[θ=0→π/3]sinθsinθdθ =4π√3∫[θ=0→π/3]sinθ^2θdθ =4π√3∫[θ=0→π/3](1/2-cos2θ/2)dθ =4π√3[θ=0→π/3][θ/2-sin2θ/4]dθ =4π√3(π/6-√3/8) =2π^2√3/3-3π/2 体積=π∫[θ=π/3→2π/3](√3/2+sinθ)^2dθ =π∫[θ=π/3→2π/3](3/4+sinθ√3+sin^2
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