Recent content by Robb

  1. R

    Show the dihedral group ##D_6## is isomorphic to ##S_3 x Z_2##

    I'm not really sure where to begin with this problem. Any insight as to where to begin or what to look out for would be much appreciated! Orders of ##S_3## ##|e|=1## ##|f|=3## ##|f^2|=2## ##|g|=2## ##|gf|=2## ##|gf^2|=3## Orders of ##Z_2## ##|0|=1## ##|1|=2## Orders of ##S_3 x Z_2##...
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    Show N is a normal subgroup and G/N has finite element

    Much appreciated! I think I get it.
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    Show N is a normal subgroup and G/N has finite element

    Clearly e ∈ N. If a, b ∈ N, say ##a^k = b^l = e##, for some k,l ∈ N, then ##(ab)^{kl} = (a^k )^l (b^l )^k = e^l e^k = e##; thus, ab ∈ N. Also, ##|a|=|a^{−1}|##, so ##a^{−1}## ∈ N. Thus, N is a subgroup. As G is abelian, it is normal. Take any c ∈ G. If, for some n ∈ N, we have ##(cN)^n = eN##...
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    Solving systems of equations using Jordan exchanges

    2u + 3v + 3w = 2 + 5v + 7w = 2 6u + 9v + 8w = 5 ##\begin{bmatrix} 2 & 3 & 3 & 2 \\ 0 & 5 & 7 & 2 \\ 6 & 9 & 8 & 5 \end{bmatrix}## We have been asked to use Jordan exchange to solve the above equations. Can someone please explain how to determine the values for r, s for the equations...
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    What is the structure of an H-decomposable graph?

    Thanks, I don't suppose you would have an example of the graphs G and H, and possibly the partitions?
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    What is the structure of an H-decomposable graph?

    Can someone please explain H-decomposable graphs. I understand that if all the subgraphs ##H_1, H_2, ..., H_k## are isomorphic to the same graph H, then G is H-decomposable. What I don't understand is, what is H? I'm reading this as there is a subgraph H, that contains a family of subgraphs...
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    Cubic graph containing a 1-factor

    1-factor is the same as a perfect matching-A graph G has a perfect matching iff for ##S \in V(G), k_o(G-S) \leq |S|##. If G has odd order, then G has no 1-factor. A 1-factor is a 1-regular sub-graph of G. Also, every bridgeless cubic graph contains a 1-factor as well as every cubic graph with at...
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    Cubic graph containing a 1-factor

    I understand how to show a given graph does/does not contain a 1-factor but I'm not sure how to show existence (or the lack thereof). Please advise.
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    Domination number of a graph G

    I thought it was ok. Thanks for the help..., again!
  10. R

    Domination number of a graph G

    Right, I get what you're saying. Going to revisit.
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    Domination number of a graph G

    When I asked my instructor about it she said to use partite sets. Hence, |U| = |W| = 6. One vertex from W can dominate 3 vertices in U and one vertex in U can dominate 3 vertices in W. This leaves 2 vertices in each set U and W. These must be dominated by two vertices. Hence, ##\gamma \neq 3##.
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    Construct a quadrilateral in a Poincare half plane

    FYI, attached is another option.
  13. R

    Domination number of a graph G

    ##\gamma(G) \leq 4## ##Claim: \gamma(G) = 4## Since ##\Delta(G) = 3## a vertex can dominate at most four vertices. There are eight vertices equivalent to ##\Delta(G)##, so these are dominated by two vertices. The remaining four vertices are of degree two which require two vertices to dominate...
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    Construct a quadrilateral in a Poincare half plane

    This is perfect! Thanks so much. Makes sense. I didn't consider sending y to infinity. Good day, my friend!
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