Draw a figure with 4 sides. How many diagonals does it have? (2)
Draw a figure with 5 sides. How many diagonals does it have? (5)
Draw a figure with 6 sides. How many diagonals does it have? (9)
Find a pattern to see that a 10-sided figure (decagon) has (10*7)/2 = 35 diagonals. We used the free website www.geogebra.org for our drawings.
Video
https://youtu.be/QnRn194S338
Handout: See Thinking in Patterns Session 1 BLM 3. https://www.mapsfoundation.com/thinking-in-patterns-resources