Clarifications on using dsolve

In this we see that the answer contains a constant namely C22. If I want to extract just the function part ie 'sin(x)' without adding any condition how do I do that ?? Please help.

Answer 1

[Mischa Kim]

Hirak, one simple way would be to add another initial condition (first derivative)

 f = dsolve('D2y + y = 0','Dy(0) = 1','y(0) = 0',x)
 f =
 sin(x)