@mmcdara 

Thank you so much!!!

@Preben Alsholm 

Now I understand. Thank you so much

@acer 

Hello!

Thanks for the answers!!!

The equation comes from a problem involving nuclear power, reactivity, critical reactor ...
When I make f(0) = 0 in the problem, I am saying that the initial reactivity is zero.
In the problem in question, when t = 0.03, my reactivity is approximately +0.003.
I used several numerical methods, including CK45, but I was unable to get the solution for f(t) with any of them. I can't get out of the singularity!!!

Thank you to change the Post to Question!!!

Ivi