※ 引述《momolo2000 (氣球緩緩升起伴隨著我的)》之銘言：
: 如題
: https://i.imgur.com/ZxT61Y0h.jpg
: 算了很久都沒有辦法導出來，有沒有高手可以幫忙?
: 解答者送100p幣，感激不盡
要守承諾喔
S' = -k[S - S_i]
令A = S - S_i
A' = -kA
=> lnA = -kt + c
=> A = Cexp(-kt)
=> S = S_i + Cexp(-kt)
IC：S(0) = 1
=> 1 = S_i + C => C = 1 - S_i
=> S(t) = S_i + (1 - S_i)exp(-kt)
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