Ok, I solved it.
I got f(0) = 3. Is that right?
I then have another problem:
f(x) = definite integral from 0 to x : sin(t) / (t+1) dt.
1) Find where f(x) has local maximum and minimum values (I should not find the function values).
A more interesting one:
2) Show that f(x) > 0, when x > 0. (Here I should use integration by parts...)
Do anyone want to help? :-)