Originally Posted by

**astuart** I'm having a little trouble figuring out how to calculate the derivative of a logistic function.

$\displaystyle {\left(\frac{3000}{1 + 9e^{-0.4055t}}\right)} $

I'm starting to feel like this 'introduction to calculus' is a little bit above me, but oh well.

I originally just used the quotient rule, $\displaystyle {\left(\frac{g(t)f '(t) - f(t)g '(t)}{(g(t))^2}\right)}$

with $\displaystyle f(t)=3000... f '(t)= 0.... g(t)= 1 + 9e^{-0.4055t}.... g '(t)= 3.6495e^{-0.4055t}$

Using those figures there, I ended up with

$\displaystyle {\left(\frac{0 - 29,192}{7.71}\right)}$ when solving for t=4.

Where am I going wrong?