# Difference between revisions of "Graphs And Polyhedra"

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# Concept Map

Error: Mind Map file `Graphs And Polyhedrons.mm` not found

# Teaching Outlines

1. Defining a Graph, node arc and Region
2. Framing Euler's Formula for graphs
3. Verifying Euler's Formula N + R = A + 2 for given Plane graphs
4. Drawing graphs for given N,R and A
5. Identifying the Traversible graphs
6. Explaining and using the condition for Traversible graphs
7. defining a Polyhedra
8. Framing Euler's formula for Polyhedra
9. verifying Euler's formula for the given Polyhedra

## Concept

Representation of a Graph

### Learning objectives

1. To define what is node.
2. to define what is arc
3. To define what is Region
4. To represent a Graph with node, Arc and Regions

### Notes for teachers

These are short notes that the teacher wants to share about the concept, any locally relevant information, specific instructions on what kind of methodology used and common misconceptions/mistakes.

### Activities

1. Activity No #1

# Introduction to Graphs

1. Activity No #2

# Graph Theory

## Concept #

### Notes for teachers

These are short notes that the teacher wants to share about the concept, any locally relevant information, specific instructions on what kind of methodology used and common misconceptions/mistakes.

### Activities

1. Activity No #1
2. Activity No #2

# Hints for difficult problems

Statement : The Königsberg bridge problem : if the seven bridges of the city of Königsberg (left figure; Kraitchik 1942), formerly in Germany but now known as Kaliningrad and part of Russia, over the river Preger can all be traversed in a single trip without doubling back, with the additional requirement that the trip ends in the same place it began. This is equivalent to asking if the multigraph on four nodes and seven edges (right figure) has an Eulerian cycle. This problem was answered in the negative by Euler (1736), and represented the beginning of graph theory. Image Courtesy : http://mathworld.wolfram.com/KoenigsbergBridgeProblem.html

Interpretation :

For Konigsberg, let us represent land with red dots and bridges with black curves, or arcs:

Thus, in its stripped down version, the seven bridges problem looks like this:

The problem now becomes one of drawing this picture without retracing any line and without picking your pencil up off the paper. Consider this: all four of the vertices in the above picture have an odd number of arcs connected to them. Take one of these vertices, say one of the ones with three arcs connected to it. Say you're going along, trying to trace the above figure out without picking up your pencil. The first time you get to this vertex, you can leave by another arc. But the next time you arrive, you can't. So you'd better be through drawing the figure when you get there! Alternatively, you could start at that vertex, and then arrive and leave later. But then you can't come back. Thus every vertex with an odd number of arcs attached to it has to be either the beginning or the end of your pencil-path. So you can only have up to two 'odd' vertices! Thus it is impossible to draw the above picture in one pencil stroke without retracing.

# Math Fun

Usage

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