If L is decidable and acceptable, is L' (complementary language) not-acceptable? I know that if L is decidable and L' is acceptable, than L is not-acceptable.
Is it also true to say that if L is decidable and acceptable, than L' is not-acceptable?
I'm sorry if this question sounds dumb, but I have a test on these stuff in 2 days and I just wanna be 100% sure.

Your initial statement

if L is decidable and L' is acceptable, then L is not-acceptable 

Is incorrect.  If L is decidable, then L' is also decidable, because the decidable languages are closed under complement.  Since every decidable language is also acceptable, the above statement is incorrect.
Consequently, the statement

if L is decidable and acceptable, then L' is not-acceptable

Is also incorrect, because if L is decidable, so is L'.  Consequently, L' is acceptable as well.
