Let G be a graph embedded to a surface such that all faces of G are triangular. Such an embedding is called triangulation. Exercise (***). Generalize the examples to prove that the spectra of G* and M(G) are equal, except possibly the eigenvalue {6}. σ ( G ∗ ) ∖ { 6 } = σ ( M ( G ) ) ∖ { 6 } {\displaystyle \sigma (G^{*})\backslash \{6\}=\sigma (M(G))\backslash \{6\}}