Abstract Algebra 2016 – BSc Computer Science Part 2 (MJPRU)
Paper code: 13511
1511
B.Sc. (Computer Science) (Part 2)
Examination, 2016
Paper No. 1.2
ABSTRACT ALGEBRA
Time: Three Hours] [Maximum Marks: 50
Note: Attempt five questions in all selecting at least one question from each Section. All questions carry equal marks.
Section-A
1. (a) Show that the set of matrices:
Where 
(b) Show that the set of all positive rational numbers form an abelian group under the composition defined by:
2. (a) Show that every permutation can be expressed as product of disjoint cycles.
(b) Show that a necessary and sufficient condition for a non-empty subset of a group G to be a subgroup is that:
Section-B
3. (a) State and prove Lagrange’s theorem.
(b) Use Fermat’s theorem to determine the remainder, if 
4. (a) Show the every subgroup of a cyclic group is cyclic.
(b) Prove that the intersection of any two normal subgroups of a group is a normal subgroup.
Section-C
5. (a) Show that the set R={0,1,2,3,4,5} is a commutative ring with respect to 
(b) Prove that ever field is an internal domain.
6. (a) If f is a homomorphism of a ring R into a ring R’ with kernel S, then show that S is an ideal of R.
(b) State and prove Fundamental theorem on homomorphism of rings.
Ssection-D
7. (a) Show that S is an ideal of S+T, where S is any ideal of ring R, and T any sub-ring of R.
(b) Prove that the necessary and sufficient condition that the non-zero element a in the Euclidean ring R is a unit is that d(a)=d(1).
8. Define maximal ideal and shown that an ideal S of a ring R with unity is maximal if an only if the residue class ring R/S is a field.
Section-E
9. (a) Show that the union of two sub-spaces is a subspace if and only if one is contained in the other.
(b) If 
10. If 
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