# Course:Harris, Fall 07: Diary Week 2

From EscherMath

(short week)

Wed:

- collected Polygon Exercises
- class finished up last week's Tessellations Exploration (~20 mintues), turned it in
- took first look at Kali (~20 minutes), considering what different types of symmetry were being created
- started working on Symmetry of Stars Exploration, but didn't finish

Fri:

- spent most of the class (~30 min) delving into #3 of last week's Exercises:
- why triangle angle-sum is 180 (opposite interior angles)
- why quadrilateral angle-sum is 360 (two interior triangles)
- why one has to be careful with diagonals for non-convex quadrilaterals

- why, in a quadrilateral, opposite angles being congruent implies opposites are parallel
- need to get to opposite interior angles
- that means need to show adjacent angles add to 180
- how to get to that by using quadrilateral angle-sum is 360

- class finished up Symmetry of Stars Exploration
- just began to discuss Rotational and Reflectional Symmetries in Escher Exploration