※ 引述《chris100466 (chris)》之銘言：
: 想請問這題怎麼求得k值，謝謝
: http://i.imgur.com/5LV7rY2.jpg
25 = (4 / k)[1 - exp(-10k)]
=> (25 / 4)kexp(10k) - exp(10k) = -1
=> 10(k - (4/25))exp(10(k - (4/25)))= -(40 / 25)exp(-40/25) > -1
W = 10(k - 4/25), Wexp(W) = -(8/5)exp(-8/5)
=> W(-(8/5)exp(-8/5)) = 10(k - 4/25)
=> k = (1/10)W[-(8/5)exp(-8/5)] + 4/25
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