How boundary conditions help in finding integration constant

[gracy]

How to find value of integration constant?I know with the help of boundary conditions,but How boundary conditions help in finding integration constant?

 

[blue_leaf77]

An integral $I$ without integration limits is an indefinite integral
$$
I(x) = \int f(x) dx = F(x) + C
$$
If you know at least one boundary condition, e.g. $I(x)$ at $x=a$, you can plug in these values to get
$$
I(a) = F(a) + C
$$
which can be solved for C.