# 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 is a real number, forms a group under matrix multiplication?

(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 is divided by *103*.

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 and as two ring compositions.

(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 and are two vector V(F), and , show that the set is linearly dependent.

10. If and are two sub-spaces of a finite dimensional vector space V(F), then: .

……..**End**……..