We know that the only way we get a constant function as a result of a derivative is if the function is a linear function. A general linear function is given by:
[tex]f(x)=mx+b[/tex]
In this case we know the result is c, which means that m has to be c and since n is the other constant label we need to use we conclude that b is n. Therefore, the antiderivative is:
[tex]f(x)=cx+n[/tex]
