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åå¼=â2a³Ãâ«(-Ï,Ï)(1-cost)^(5/2)dt
=2â2a³â«(0,Ï)(1-cost)^(5/2)dt
=2â2a³â«(0,Ï)(2sin²t/2)^(5/2)dt
令t/2=u
åå¼=4â2a³â«(0,Ï/2)(2sin²u)^(5/2)du
=32a³â«(0,Ï/2)(sinu)^5du
=32a³Ã4/5Ã2/3Ã1
=256a³/15.
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