求∫(0,2π)2(t- sint)^?
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∫[0,2π] 2(t-sint)(1-cost)^2 dt
= ∫[0,2π] (1-cost) d(t-sint)^2
= [0,2π] (1-cost) (t-sint)^2 - ∫[0,2π] (t-sint)^2 sint dt
= ∫[0,2π] (t-sint)^2 dcost
= [0,2π] (t-sint)^2 cost - ∫[0,2π] cost 2(t-sint)(1-cost) dt
= 4π^2 - ∫[0,2π] cost 2(t-sint)(1-cost) dt (第二项展开后对各项分别求积分)
= 4π^2 + 2π^2
= 6π^2
= ∫[0,2π] (1-cost) d(t-sint)^2
= [0,2π] (1-cost) (t-sint)^2 - ∫[0,2π] (t-sint)^2 sint dt
= ∫[0,2π] (t-sint)^2 dcost
= [0,2π] (t-sint)^2 cost - ∫[0,2π] cost 2(t-sint)(1-cost) dt
= 4π^2 - ∫[0,2π] cost 2(t-sint)(1-cost) dt (第二项展开后对各项分别求积分)
= 4π^2 + 2π^2
= 6π^2
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