December 1999
MA214 : DISCRETE MATHEMATICS

QUESTION 4

Total Marks: 15 Marks

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Question 4

(a)

Show that every tree with at least two vertices has at least one vertex of odd degree.

If every vertex were of even degree then since trees are connected (one mark )the tree would have an Euler cycle (one mark ). Since trees have no cycles at all,this cannot happen (one mark ).

 

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(b)

The following is an adjacency matrix of a graph. Draw the graph.

Three marks,subtract one for each mistake up to a maximum of three.

 

[3]
(c)

Consider the graph shown below.

(i)Write down the distance matrix.[2 marks ]

Two marks, Subtract one for each mistake up to a maximum of two.

(ii)Define a walk, a trail and an Eulerian trail of a graph .Find an Eulerian trail in the given graph.[4 marks ]

A walk is a sequence of vertices of G where is an edge of G. One mark .
A trail is a walk in which the edges are distinct One mark .
A Eulerian trail is a trail that includes each edge of the graph One mark .
Eulerian trail:41523576 or 41532576 One mark .

 

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(d)

Consider the directed graph shown below.

Write down the adjacency matrix for this graph.

Three marks, subtract one for each mistake up to a maximum of three.

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