In the page before we demonstrated that the first order linear differential equation :

Has this solution :

In physics and especially in electronics we will find easily functions like that below :

this differential equation is a simpler case of our generic.

P(x)=a

Q(x)=b

We notice that

C1 can be set to zero since we already have a constant C

Resuming

(A)

(B)

The (B) solution will be heavily used in this site since it is extremely useful.