# Crazy 2nd derivative problem

#### greko

I am not sure if this counts as homework but its a complex problem to me. I must find the inflection point of the equation (c/((1+ae^(-bx)))). Therefore I must take the 2nd derivative. Which I got as (abc)(e^(-bx))(abe^(-bx)-b)/((1+ae^(-bx))^7)). And this sounds wrong to me? Can someone tell me if I am on the right track?

#### phyzguy

Science Advisor
I think you're on the right track. The 7th power in the denominator should just be a 3rd power, though - was this a typo, or did you make a mistake? Now what does this equal at the inflection point?

#### Mu naught

You actually should be able to find the inflection point using only the first derivative. Set the derivative equal to zero and then test points on both sides of each zero. If you get matching signs on both sides of a critical point then you have an inflection.

#### Office_Shredder

Staff Emeritus
Science Advisor
Gold Member
You actually should be able to find the inflection point using only the first derivative. Set the derivative equal to zero and then test points on both sides of each zero. If you get matching signs on both sides of a critical point then you have an inflection.
Inflection points don't have to be critical points

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