The most difficult part of the rest of this section was just wrapping my mind around two of the examples. In the example on the top of page 170 I don't think I understand why the set of these matrices is a group only if ad-bc is not 0. I also couldn't quite wrap my mind around the Cartesian product of a group of number and a dihedral group.
So far I am enjoying groups. They seem to mostly just be classifications of things that I already knew about. When you said on Friday that we would be learning about dihedral groups on Monday I was a little freaked out. I was pleasantly pleased that dihedral groups are just rotations and translations of polygons on a plane, which is simple enough.
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