S1 : { (a^n)^m | n<=m>=0} => { (a^n)^m | n,m>=0 & m>=n}
=> { ɛ ,a,aa,aaa,........}
so,Regular Expression for S1 will be a*
S2 : { a^nb^n | n>=1} U { a^nb^m | n>=1,m>=1}
=> {ab,aabb,aaabbb,...} U {ab,aab,abb,aabb,......} => {ab,aab,abb,aabb,......}
so,Regular Expression for S2 will be a+b+
Therefore both S1 and S2 are Regular.