Re: [微積] 積分求救
※ 引述《whatsgogo (Hi, there!)》之銘言：
: http://ppt.cc/3yWl
: 求版上高手相救~
: 我積了好多次 都等於0耶
: 多謝大家了:)
let u = 1 - r/R --> r = R(1-u), du = -dr/R
R 1/7 r=R 1/7 2 2 8/7 1/7
∫(1 - r/R) rdr = ∫u R (u-1)du = R ∫(u - u )du
0 r=0
2 7 15/7 7 8/7 r=R 2 7 7 49 2
= R (--- u - --- u )| = R (--- - ---) = --- R
15 8 r=0 8 15 120
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