Let's see it this way, if you have where C and k are real numbers, derivating:

Then is the anti-derivative of

That's denoted as follows:

To find the anti-derivative you need (there are an infinit number of them) you have to find the constant k, and for that you use the other information you have

Read here:

http://www.mathhelpforum.com/math-he...66-post12.html