Logistic Function

I'm doing my Maths SL IA Type II - Population trends in China.

A logistic function will never reach it's upper bound, it will be an asymptote, continuing to infinity.
But does it start at zero? Or does the bottom half of the sigmoid curve continue to infinity too?

Thanks

As x approaches infinity logx or lnx approaches infinity.

As x approaches 0 lnx approaches negative infinity. This makes sense if you consider that logs are just exponents. That is you cannot raise a positive base to any power to make it a negative number.

e^y = x

lnx = y

x can never be negative as e is postive.

So X will never be negative, but can it reach zero?

Can 0 = e^y ?

remember if y = 0 then e^y = 1 and if y = -1 then e^y = 1/e

Is there any y that makes e^y zero?

...1?

e^1 = e

You can't think of one because it does not exist. When x = 0 lnx is undefined.

You cannot raise a postive number to the power of anything and get it to equal 0 or be negative.

As x gets smaller and smaller and smaller lnx approaches negative infinity.

Watch some vids on the khan academy on limits, will make more sense then.

Oh, I see. Kind of.
Thanks