Complement of a^nb^n ={a^nb^m : m!=n } U { (aUb)*ba(aUb)*}
The given language is Deterministic CFL and not regular and the complement is also a DCFL and not regular language because DCFL is closed under complementation.
ii)Complement of a^nb^nc^n =a*b*c* - (a^n b^n c^n: n>=0)
= a*b*c* INTERSECT {(a^i b^j c^k|i=j)' U (a^i b^j c^k | j=k)'}
= a*b*c* INTERSECT (a^i b^j c^k|i=j)' U a*b*c* INTERSECT (a^i b^j c^k|j=k)'
= (a^i b^j c^k|i!=j) U (a^i b^j c^k|j!=k)
L={a^nb^nc^n,n>=0} is a NPDA but the complement is CFL and not regular