First, you went to all that trouble to find 6/13. Why did you discard it for the CDF?
CDF needs a LOT of work and there appears to be quite a bit of understanding missing. You studied indefinite integrals for a reason. You seem to have forgotten what they are.
. You absolutely must NOT ignore that arbitrary constant.
Your task is to find the value of C such that You tell me why.
Similarly, you must find the value of D, such that Again, where did that come from?